This chapter describes a set of atomic work products that are created when developing an architecture. An artifact represents an individual model of a system or solution, which could potentially be re-used in a variety of contexts. An artifact is distinct from a deliverable, which is a contracted output from a project. In general cases, deliverables will contain artifacts and each artifact may exist in many deliverables.

This chapter discusses the concepts surrounding architecture artifacts and then goes on to discuss the artifacts that are created at each phase within the Architecture Development Method (ADM).

35.1 Basic Concepts

Architectural artifacts are created in order to describe a system, solution, or state of the enterprise. The concepts discussed in this section have been adapted from more formal definitions contained in ISO/IEC 42010:2007 and illustrated in Basic Architectural Concepts . ¹

Note:

The notation used is from the Unified Modeling Language (UML) specification.

A "system" is a collection of components organized to accomplish a specific function or set of functions.

The "architecture" of a system is the system's fundamental organization, embodied in its components, their relationships to each other and to the environment, and the principles guiding its design and evolution.

An "architecture description" is a collection of artifacts that document an architecture. In TOGAF, architecture views are the key artifacts in an architecture description.

"Stakeholders" are people who have key roles in, or concerns about, the system; for example, as users, developers, or managers. Different stakeholders with different roles in the system will have different concerns. Stakeholders can be individuals, teams, or organizations (or classes thereof).

"Concerns" are the key interests that are crucially important to the stakeholders in the system, and determine the acceptability of the system. Concerns may pertain to any aspect of the system's functioning, development, or operation, including considerations such as performance, reliability, security, distribution, and evolvability.

A "view" is a representation of a whole system from the perspective of a related set of concerns.

In capturing or representing the design of a system architecture, the architect will typically create one or more architecture models, possibly using different tools. A view will comprise selected parts of one or more models, chosen so as to demonstrate to a particular stakeholder or group of stakeholders that their concerns are being adequately addressed in the design of the system architecture.

A "viewpoint" defines the perspective from which a view is taken. More specifically, a viewpoint defines: how to construct and use a view (by means of an appropriate schema or template); the information that should appear in the view; the modeling techniques for expressing and analyzing the information; and a rationale for these choices (e.g., by describing the purpose and intended audience of the view).

• A view is what you see. A viewpoint is where you are looking from - the vantage point or perspective that determines what you see.
• Viewpoints are generic, and can be stored in libraries for re-use. A view is always specific to the architecture for which it is created.
• Every view has an associated viewpoint that describes it, at least implicitly. ISO/IEC 42010:2007 encourages architects to define viewpoints explicitly. Making this distinction between the content and schema of a view may seem at first to be an unnecessary overhead, but it provides a mechanism for re-using viewpoints across different architectures.

In summary, then, architecture views are representations of the overall architecture in terms meaningful to stakeholders. They enable the architecture to be communicated to and understood by the stakeholders, so they can verify that the system will address their concerns.

Note:

The terms "concern" and "requirement" are not synonymous. A concern is an area of interest. So, system reliability might be a concern/area of interest for some stakeholders. The reason why architects should identify concerns and associate them with viewpoints, is to ensure that those concerns will be addressed in some fashion by the models of the architecture. For example, if the only viewpoint selected by an architect is a structural viewpoint, then reliability concerns are almost certainly not being addressed, since they cannot be represented in a structural model. Within that concern, stakeholders may have many distinct requirements: different classes of users may have very different reliability requirements for different capabilities of the system.

Concerns are the root of the process of decomposition into requirements. Concerns are represented in the architecture by these requirements. Requirements should be SMART (e.g., specific metrics).

35.1.1 Simple Example of a Viewpoint and View

For many architectures, a useful viewpoint is that of business domains, which can be illustrated by an example from The Open Group itself.

The viewpoint is specified as follows:

The corresponding view of The Open Group (in 2008) is shown in Example View - The Open Group Business Domains in 2008 .

35.2 Developing Views in the ADM

35.2.1 General Guidelines

The choice of which particular architecture views to develop is one of the key decisions that the architect has to make.

The architect has a responsibility for ensuring the completeness (fitness-for-purpose) of the architecture, in terms of adequately addressing all the pertinent concerns of its stakeholders; and the integrity of the architecture, in terms of connecting all the various views to each other, satisfactorily reconciling the conflicting concerns of different stakeholders, and showing the trade-offs made in so doing (as between security and performance, for example).

The choice has to be constrained by considerations of practicality, and by the principle of fitness-for-purpose (i.e., the architecture should be developed only to the point at which it is fit-for-purpose, and not reiterated ad infinitum as an academic exercise).

As explained in Part II: Architecture Development Method (ADM), the development of architecture views is an iterative process. The typical progression is from business to technology, using a technique such as business scenarios (see Part III, 26. Business Scenarios) to properly identify all pertinent concerns; and from high-level overview to lower-level detail, continually referring back to the concerns and requirements of the stakeholders throughout the process.

Moreover, each of these progressions has to be made for two distinct environments: the existing environment (referred to as the baseline in the ADM) and the target environment. The architect must develop pertinent architecture views of both the Baseline Architecture and the Target Architecture. This provides the context for the gap analysis at the end of Phases B, C, and D of the ADM, which establishes the elements of the Baseline Architecture to be carried forward and the elements to be added, removed, or replaced.

This whole process is explained in Part III, 27. Gap Analysis .

35.2.2 View Creation Process

As mentioned above, at the present time TOGAF encourages but does not mandate the use of ISO/IEC 42010:2007. The following description therefore covers both the situation where ISO/IEC 42010:2007 has been adopted and where it has not.

ISO/IEC 42010:2007 itself does not require any specific process for developing viewpoints or creating views from them. Where ISO/IEC 42010:2007 has been adopted and become well-established practice within an organization, it will often be possible to create the required views for a particular architecture by following these steps:

1. Refer to an existing library of viewpoints
2. Select the appropriate viewpoints (based on the stakeholders and concerns that need to be covered by views)
3. Generate views of the system by using the selected viewpoints as templates

This approach can be expected to bring the following benefits:

• Less work for the architects (because the viewpoints have already been defined and therefore the views can be created faster)
• Better comprehensibility for stakeholders (because the viewpoints are already familiar)
• Greater confidence in the validity of the views (because their viewpoints have a known track record)

However, situations can always arise in which a view is needed for which no appropriate viewpoint has been predefined. This is also the situation, of course, when an organization has not yet incorporated ISO/IEC 42010:2007 into its architecture practice and established a library of viewpoints.

In each case, the architect may choose to develop a new viewpoint that will cover the outstanding need, and then generate a view from it. (This is ISO/IEC 42010:2007 recommended practice.) Alternatively, a more pragmatic approach can be equally successful: the architect can create an ad hoc view for a specific system and later consider whether a generalized form of the implicit viewpoint should be defined explicitly and saved in a library, so that it can be re-used. (This is one way of establishing a library of viewpoints initially.)

Whatever the context, the architect should be aware that every view has a viewpoint, at least implicitly, and that defining the viewpoint in a systematic way (as recommended by ISO/IEC 42010:2007) will help in assessing its effectiveness; i.e., does the viewpoint cover the relevant stakeholder concerns?.

35.3 Views, Tools, and Languages

The need for architecture views, and the process of developing them following the ADM, are explained above. This section describes the relationships between architecture views, the tools used to develop and analyze them, and a standard language enabling interoperability between the tools.

35.3.1 Overview

In order to achieve the goals of completeness and integrity in an architecture, architecture views are usually developed, visualized, communicated, and managed using a tool.

In the current state of the market, different tools normally have to be used to develop and analyze different views of the architecture. It is highly desirable that an architecture description be encoded in a standard language, to enable a standard approach to the description of architecture semantics and their re-use among different tools.

A viewpoint is also normally developed, visualized, communicated, and managed using a tool, and it is also highly desirable that standard viewpoints (i.e., templates or schemas) be developed, so that different tools that deal in the same views can interoperate, the fundamental elements of an architecture can be re-used, and the architecture description can be shared among tools.

Issues relating to the evaluation of tools for architecture work are discussed in detail in Part V, 42. Tools for Architecture Development .

35.4 Views and Viewpoints

35.4.1 Example of Views and Viewpoints

To illustrate the concepts of views and viewpoints, consider the example of a very simple airport system with two different stakeholders: the pilot and the air traffic controller.

One view can be developed from the viewpoint of the pilot, which addresses the pilot's concerns. Equally, another view can be developed from the viewpoint of the air traffic controller. Neither view completely describes the system in its entirety, because the viewpoint of each stakeholder constrains (and reduces) how each sees the overall system.

The viewpoint of the pilot comprises some concerns that are not relevant to the controller, such as passengers and fuel, while the viewpoint of the controller comprises some concerns not relevant to the pilot, such as other planes. There are also elements shared between the two viewpoints, such as the communication model between the pilot and the controller, and the vital information about the plane itself.

A viewpoint is a model (or description) of the information contained in a view. In our example, one viewpoint is the description of how the pilot sees the system, and the other viewpoint is how the controller sees the system.

Pilots describe the system from their perspective, using a model of their position and vector toward or away from the runway. All pilots use this model, and the model has a specific language that is used to capture information and populate the model.

Controllers describe the system differently, using a model of the airspace and the locations and vectors of aircraft within the airspace. Again, all controllers use a common language derived from the common model in order to capture and communicate information pertinent to their viewpoint.

Fortunately, when controllers talk with pilots, they use a common communication language. (In other words, the models representing their individual viewpoints partially intersect.) Part of this common language is about location and vectors of aircraft, and is essential to safety.

So in essence each viewpoint is an abstract model of how all the stakeholders of a particular type - all pilots, or all controllers - view the airport system.

Tools exist to assist stakeholders, especially when they are interacting with complex models such as the model of an airspace, or the model of air flight.

The interface to the human user of a tool is typically close to the model and language associated with the viewpoint. The unique tools of the pilot are fuel, altitude, speed, and location indicators. The main tool of the controller is radar. The common tool is a radio.

To summarize from the above example, we can see that a view can subset the system through the perspective of the stakeholder, such as the pilot versus the controller. This subset can be described by an abstract model called a viewpoint, such as an air flight versus an air space model. This description of the view is documented in a partially specialized language, such as "pilot-speak" versus "controller-speak". Tools are used to assist the stakeholders, and they interface with each other in terms of the language derived from the viewpoint ("pilot-speak" versus' "controller-speak").

When stakeholders use common tools, such as the radio contact between pilot and controller, a common language is essential.

35.4.2 Views and Viewpoints in Enterprise Architecture

Now let us map this example to the enterprise architecture. Consider two stakeholders in a new small computing system: the users and the developers.

The users of the system have a viewpoint that reflects their concerns when interacting with the system, and the developers of the system have a different viewpoint. Views that are developed to address either of the two viewpoints are unlikely to exhaustively describe the whole system, because each perspective reduces how each sees the system.

The viewpoint of the user is comprised of all the ways in which the user interacts with the system, not seeing any details such as applications or Database Management Systems (DBMS).

The viewpoint of the developer is one of productivity and tools, and doesn't include things such as actual live data and connections with consumers.

However, there are things that are shared, such as descriptions of the processes that are enabled by the system and/or communications protocols set up for users to communicate problems directly to development.

In this example, one viewpoint is the description of how the user sees the system, and the other viewpoint is how the developer sees the system. Users describe the system from their perspective, using a model of availability, response time, and access to information. All users of the system use this model, and the model has a specific language.

Developers describe the system differently than users, using a model of software connected to hardware distributed over a network, etc. However, there are many types of developers (database, security, etc.) of the system, and they do not have a common language derived from the model.

35.4.3 Need for a Common Language and Interoperable Tools for Architecture Description

Tools exist for both users and developers. Tools such as online help are there specifically for users, and attempt to use the language of the user. Many different tools exist for different types of developers, but they suffer from the lack of a common language that is required to bring the system together. It is difficult, if not impossible, in the current state of the tools market to have one tool interoperate with another tool.

Issues relating to the evaluation of tools for architecture work are discussed in detail in Part V, 42. Tools for Architecture Development .

35.5 Conclusions

This section attempts to deal with views in a structured manner, but this is by no means a complete treatise on views.

In general, TOGAF embraces the concepts and definitions presented in ISO/IEC 42010:2007, specifically the concepts that help guide the development of a view and make the view actionable. These concepts can be summarized as:

• Selecting a key stakeholder
• Understanding their concerns and generalizing/documenting those concerns
• Understanding how to model and deal with those concerns

In the following sections, TOGAF presents some recommended viewpoints, some or all of which may be appropriate in a particular architecture development. This is not intended as an exhaustive set of viewpoints, but simply as a starting point. Those described may be supplemented by additional viewpoints as required. These TOGAF sections on viewpoints should be considered as guides for the development and treatment of a view, not as a full definition of a viewpoint.

35.6 Taxonomy of Architecture Viewpoints

TOGAF defines a set of architecture viewpoints that may be adopted, enhanced, and combined to produce views that describe an architecture. In order to aid in re-use and consistency, a number of atomic viewpoints are outlined below that enable the development of individual views for many different purposes. In a typical enterprise, stakeholder concerns will be identified in order to develop richer and more complex viewpoints that address specific stakeholder groups.

Part III, 24. Stakeholder Management provides an outline of the major stakeholder groups that are typically encountered when developing enterprise architecture. The likely concerns of each stakeholder group are also identified.

Viewpoints Associated with the Core Content Metamodel and Extensions shows the viewpoints that are associated with the core content metamodel and each of the content extensions.

The specific classes of viewpoint are as follows:

• Catalogs are specific foundational viewpoints that represent lists of building blocks.
• Matrices are specific foundational viewpoints that show the relationships between building blocks of specific types.
• Diagrams are graphical viewpoints that present building blocks in a rich and visual way, more suited to stakeholder communication.

The TOGAF architecture domains are themselves viewpoints that can be used to group the foundational catalogs, matrices, and diagrams:

• The Business Architecture domain addresses the needs of users, planners, and business management.
• The Data Architecture domain addresses the needs of database designers, database administrators, and system engineers.
• The Application Architecture domain addresses the needs of system and software engineers.
• The Technology Architecture domain addresses the needs of acquirers, operators, administrators, and managers.

When applying TOGAF within a particular enterprise or project, it may be necessary to take each one of these stakeholder types (e.g., user, database administrator, acquirer, etc.) and create an explicit set of stakeholder concerns. These concerns can then be used to refine and enhance the basic viewpoints provided by TOGAF.

It is expected that, when applying TOGAF to a specific architectural problem, a number of tailoring steps should take place:

• The viewpoints provided should be customized to create a set of architecture views that ensure all stakeholder concerns are met. For example, selection of core and extension content identified within Business Architecture allows for a lightweight or detailed view of Business Architecture.
• New viewpoints and views should be created to address specific needs of the problem. For example, an Enterprise Security view could be created that spans Business, Data, Application, and Technology Architecture to show security from all aspects.

35.7 Viewpoints in the Preliminary Phase

The following catalogs, matrices, and diagrams may be produced in the Preliminary phase.

• Catalogs:
  • Principles catalog
• Matrices:
  • No matrices are defined to be created during the Preliminary phase.
• Core diagrams:
  • No core diagrams are defined to be created during the Preliminary phase.
• Extension diagrams:
  • No extension diagrams are defined to be created during the Preliminary phase.

The following describes each of the catalogs, matrices, and diagrams created within the Preliminary phase.

Principles Catalog

The Principles catalog captures principles of the business and architecture principles that describe what a "good" solution or architecture should look like. Principles are used to evaluate and agree an outcome for architecture decision points. Principles are also used as a tool to assist in architectural governance of change initiatives.

The Principles catalog contains the following metamodel entities:

• Principle

35.8 Viewpoints in Phase A

The following catalogs, matrices, and diagrams may be produced in Phase A (Architecture Vision).

• Catalogs:
  • No catalogs are defined to be created during Phase A.
• Matrices:
  • Stakeholder Map matrix
• Core diagrams:
  • Value Chain diagram
  • Solution Concept diagram
• Extension diagrams:
  • No extension diagrams are defined to be created during Phase A.

The following describes each of the catalogs, matrices, and diagrams created within Phase A (Architecture Vision).

Stakeholder Map Matrix

The purpose of the Stakeholder Map matrix is to identify the stakeholders for the architecture engagement, their influence over the engagement, and their key questions, issues, or concerns that must be addressed by the architecture framework.

Understanding stakeholders and their requirements allows an architect to focus effort in areas that meet the needs of stakeholders (see Part III, 24. Stakeholder Management).

Due to the potentially sensitive nature of stakeholder mapping information and the fact that the Architecture Vision phase is intended to be conducted using informal modeling techniques, no specific metamodel entities will be used to generate a stakeholder map.

Value Chain Diagram

A Value Chain diagram provides a high-level orientation view of an enterprise and how it interacts with the outside world. In contrast to the more formal Functional Decomposition diagram developed within Phase B (Business Architecture), the Value Chain diagram focuses on presentational impact.

The purpose of this diagram is to quickly on-board and align stakeholders for a particular change initiative, so that all participants understand the high-level functional and organizational context of the architecture engagement.

Solution Concept Diagram

A Solution Concept diagram provides a high-level orientation of the solution that is envisaged in order to meet the objectives of the architecture engagement. In contrast to the more formal and detailed architecture diagrams developed in the following phases, the solution concept represents a "pencil sketch" of the expected solution at the outset of the engagement.

This diagram may embody key objectives, requirements, and constraints for the engagement and also highlight work areas to be investigated in more detail with formal architecture modeling.

The purpose of this diagram is to quickly on-board and align stakeholders for a particular change initiative, so that all participants understand what the architecture engagement is seeking to achieve and how it is expected that a particular solution approach will meet the needs of the enterprise.

35.9 Viewpoints in Phase B

The following catalogs, matrices, and diagrams may be produced in Phase B (Business Architecture).

• Catalogs:
  • Organization/Actor catalog
  • Driver/Goal/Objective catalog
  • Role catalog
  • Business Service/Function catalog
  • Location catalog
  • Process/Event/Control/Product catalog
  • Contract/Measure catalog
• Matrices:
  • Business Interaction matrix
  • Actor/Role matrix
• Core diagrams:
  • Business Footprint diagram
  • Business Service/Information diagram
  • Functional Decomposition diagram
  • Product Lifecycle diagram
• Extension diagrams:
  • Goal/Objective/Service diagram
  • Use-case diagram
  • Organization Decomposition diagram
  • Process Flow diagram
  • Event diagram

The following describes each of the catalogs, matrices, and diagrams created within Phase B (Business Architecture).

Organization/Actor Catalog

The purpose of the Organization/Actor catalog is to capture a definitive listing of all participants that interact with IT, including users and owners of IT systems.

The Organization/Actor catalog can be referenced when developing requirements in order to test for completeness.

For example, requirements for an application that services customers can be tested for completeness by verifying exactly which customer types need to be supported and whether there are any particular requirements or restrictions for user types.

The Organization/Actor catalog contains the following metamodel entities:

• Organization Unit
• Actor
• Location (may be included in this catalog if an independent Location catalog is not maintained)

Driver/Goal/Objective Catalog

The purpose of the Driver/Goal/Objective catalog is to provide a cross-organizational reference of how an organization meets its drivers in practical terms through goals, objectives, and (optionally) measures.

Publishing a definitive breakdown of drivers, goals, and objectives allows change initiatives within the enterprise to identify synergies across the organization (e.g., multiple organizations attempting to achieve similar objectives), which in turn allow stakeholders to be identified and related change initiatives to be aligned or consolidated.

The Driver/Goal/Objective catalog contains the following metamodel entities:

• Organization Unit
• Driver
• Goal
• Objective
• Measure (may optionally be included)

Role Catalog

The purpose of the Role catalog is to provide a listing of all authorization levels or zones within an enterprise. Frequently, application security or behavior is defined against locally understood concepts of authorization that create complex and unexpected consequences when combined on the user desktop.

If roles are defined, understood, and aligned across organizations and applications, this allows for a more seamless user experience and generally more secure applications, as administrators do not need to resort to workarounds in order to enable users to carry out their jobs.

In addition to supporting security definition for the enterprise, the Role catalog also forms a key input to identifying organizational change management impacts, defining job functions, and executing end-user training.

As each role implies access to a number of business functions, if any of these business functions are impacted, then change management will be required, organizational responsibilities may need to be redefined, and retraining may be needed.

The Role catalog contains the following metamodel entities:

• Role

Business Service/Function Catalog

The purpose of the Business Service/Function catalog is to provide a functional decomposition in a form that can be filtered, reported on, and queried, as a supplement to graphical Functional Decomposition diagrams.

The Business Service/Function catalog can be used to identify capabilities of an organization and to understand the level that governance is applied to the functions of an organization. This functional decomposition can be used to identify new capabilities required to support business change or may be used to determine the scope of change initiatives, applications, or technology components.

The Business Service/Function catalog contains the following metamodel entities:

• Organization Unit
• Business Function
• Business Service
• Information System Service (may optionally be included here)

Location Catalog

The Location catalog provides a listing of all locations where an enterprise carries out business operations or houses architecturally relevant assets, such as data centers or end-user computing equipment.

Maintaining a definitive list of locations allows change initiatives to quickly define a location scope and to test for completeness when assessing current landscapes or proposed target solutions. For example, a project to upgrade desktop operating systems will need to identify all locations where desktop operating systems are deployed.

Similarly, when new systems are being implemented, a diagram of locations is essential in order to develop appropriate deployment strategies that comprehend both user and application location and identify location-related issues, such as internationalization, localization, timezone impacts on availability, distance impacts on latency, network impacts on bandwidth, and access.

The Location catalog contains the following metamodel entities:

• Location

Process/Event/Control/Product Catalog

The Process/Event/Control/Product catalog provides a hierarchy of processes, events that trigger processes, outputs from processes, and controls applied to the execution of processes. This catalog provides a supplement to any Process Flow diagrams that are created and allows an enterprise to filter, report, and query across organizations and processes to identify scope, commonality, or impact.

For example, the Process/Event/Control/Product catalog allows an enterprise to see relationships of processes to sub-processes in order to identify the full chain of impacts resulting from changing a high-level process.

The Process/Event/Control/Product catalog contains the following metamodel entities:

• Process
• Event
• Control
• Product

Contract/Measure Catalog

The Contract/Measure catalog provides a listing of all agreed service contracts and (optionally) the measures attached to those contracts. It forms the master list of service levels agreed to across the enterprise.

The Contract/Measure catalog contains the following metamodel entities:

• Business Service
• Information System Service (optionally)
• Contract
• Measure

Business Interaction Matrix

The purpose of this matrix is to depict the relationship interactions between organizations and business functions across the enterprise.

Understanding business interaction of an enterprise is important as it helps to highlight value chain and dependencies across organizations.

The Business Interaction matrix shows the following metamodel entities and relationships:

• Organization
• Business Function
• Business Service
• Business Service communicates with Business Service relationships
• Business Service is dependent on Business Service relationships

Actor/Role Matrix

The purpose of this matrix is to show which actors perform which roles, supporting definition of security and skills requirements.

Understanding Actor-to-Role relationships is a key supporting tool in definition of training needs, user security settings, and organizational change management.

The Actor/Role matrix shows the following metamodel entities and relationships:

• Actor
• Role
• Actor performs Role relationships

Business Footprint Diagram

A Business Footprint diagram describes the links between business goals, organizational units, business functions, and services, and maps these functions to the technical components delivering the required capability.

A Business Footprint diagram provides a clear traceability between a technical component and the business goal that it satisfies, whilst also demonstrating ownership of the services identified.

A Business Footprint diagram demonstrates only the key facts linking organization unit functions to delivery services and is utilized as a communication platform for senior-level (CxO) stakeholders.

Business Service/Information Diagram

The Business Service/Information diagram shows the information needed to support one or more business services. The Business Service/Information diagram shows what data is consumed by or produced by a business service and may also show the source of information.

The Business Service/Information diagram shows an initial representation of the information present within the architecture and therefore forms a basis for elaboration and refinement within Phase C (Data Architecture).

Functional Decomposition Diagram

The purpose of the Functional Decomposition diagram is to show on a single page the capabilities of an organization that are relevant to the consideration of an architecture. By examining the capabilities of an organization from a functional perspective, it is possible to quickly develop models of what the organization does without being dragged into extended debate on how the organization does it.

Once a basic Functional Decomposition diagram has been developed, it becomes possible to layer heat-maps on top of this diagram to show scope and decisions. For example, the capabilities to be implemented in different phases of a change program.

Product Lifecycle Diagram

The purpose of the Product Lifecycle diagram is to assist in understanding the lifecycles of key entities within the enterprise. Understanding product lifecycles is becoming increasingly important with respect to environmental concerns, legislation, and regulation where products must be tracked from manufacture to disposal. Equally, organizations that create products that involve personal or sensitive information must have a detailed understanding of the product lifecycle during the development of Business Architecture in order to ensure rigor in design of controls, processes, and procedures. Examples of this would include credit cards, debit cards, store/loyalty cards, smart cards, user identity credentials (identity cards, passports, etc.).

Goal/Objective/Service Diagram

The purpose of a Goal/Objective/Service diagram is to define the ways in which a service contributes to the achievement of a business vision or strategy.

Services are associated with the drivers, goals, objectives, and measures that they support, allowing the enterprise to understand which services contribute to similar aspects of business performance. The Goal/Objective/Service diagram also provides qualitative input on what constitutes high performance for a particular service.

Business Use-Case Diagram

A Business Use-Case diagram displays the relationships between consumers and providers of business services. Business services are consumed by actors or other business services and the Business Use-Case diagram provides added richness in describing business capability by illustrating how and when that capability is used.

The purpose of the Business Use-Case diagram is to help to describe and validate the interaction between actors and their roles to processes and functions. As the architecture progresses, the use-case can evolve from the business level to include data, application, and technology details. Architectural business use-cases can also be re-used in systems design work.

Organization Decomposition Diagram

An Organization Decomposition diagram describes the links between actor, roles, and location within an organization tree.

An organization map should provide a chain of command of owners and decision-makers in the organization. Although it is not the intent of the Organization Decomposition diagram to link goal to organization, it should be possible to intuitively link the goals to the stakeholders from the Organization Decomposition diagram.

Process Flow Diagram

The purpose of the Process Flow diagram is to depict all models and mappings related to the process metamodel entity.

Process Flow diagrams show sequential flow of control between activities and may utilize swim-lane techniques to represent ownership and realization of process steps. For example, the application that supports a process step may be shown as a swim-lane.

In addition to showing a sequence of activity, process flows can also be used to detail the controls that apply to a process, the events that trigger or result from completion of a process, and also the products that are generated from process execution.

Process Flow diagrams are useful in elaborating the architecture with subject specialists, as they allow the specialist to describe "how the job is done" for a particular function. Through this process, each process step can become a more fine-grained function and can then in turn be elaborated as a process.

Event Diagram

The purpose of the Event diagram is to depict the relationship between events and process.

Certain events - such as arrival of certain information (e.g., customer submits sales order) or a certain point in time (e.g., end of fiscal quarter) - cause work and certain actions need to be undertaken within the business. These are often referred to as "business events" or simply "events" and are considered as triggers for a process. It is important to note that the event has to trigger a process and generate a business response or result.

35.10 Viewpoints in the Phase C Data Architecture

The following catalogs, matrices, and diagrams may be produced in Phase C (Data Architecture).

• Catalogs:
  • Data Entity/Data Component catalog
• Matrices:
  • Data Entity/Business Function matrix
  • System/Data matrix
• Core diagrams:
  • Class diagram
  • Data Dissemination diagram
• Extension diagrams:
  • Data Security diagram
  • Class Hierarchy diagram
  • Data Migration diagram
  • Data Lifecycle diagram

The following describes each of the catalogs, matrices, and diagrams created within Phase C (Data Architecture).

Data Entity/Data Component Catalog

The purpose of the Data Entity/Data Component catalog is to identify and maintain a list of all the data use across the enterprise, including data entities and also the data components where data entities are stored. An agreed Data Entity/Data Component catalog supports the definition and application of information management and data governance policies and also encourages effective data sharing and re-use.

The Data Entity/Data Component catalog contains the following metamodel entities:

• Data Entity
• Logical Data Component
• Physical Data Component

Data Entity/Business Function Matrix

The purpose of the Data Entity/Business Function matrix is to depict the relationship between data entities and business functions within the enterprise. Business functions are supported by business services with explicitly defined boundaries and will be supported and realized by business processes. The mapping of the Data Entity-Business Function relationship enables the following to take place:

• Assign ownership of data entities to organizations
• Understand the data and information exchange requirements business services
• Support the gap analysis and determine whether any data entities are missing and need to be created
• Define system of origin, system of record, and system of reference for data entities
• Enable development of data governance programs across the enterprise (establish data steward, develop data standards pertinent to the business function, etc.)

The Data Entity/Business Function matrix shows the following entities and relationships:

• Data Entity
• Business Function
• Data Entity relationship to owning Organization Unit

System/Data Matrix

The purpose of the System/Data matrix is to depict the relationship between systems (i.e., application components) and the data entities that are accessed and updated by them.

Systems will create, read, update, and delete specific data entities that are associated with them. For example, a CRM application will create, read, update, and delete customer entity information.

The data entities in a package/packaged services environment can be classified as master data, reference data, transactional data, content data, and historical data. Applications that operate on the data entities include transactional applications, information management applications, and business warehouse applications.

The mapping of the Application Component-Data Entity relationship is an important step as it enables the following to take place:

• Assign access of data to specific applications in the organization
• Understand the degree of data duplication within different applications, and the scale of the data lifecycle
• Understand where the same data is updated by different applications
• Support the gap analysis and determine whether any of the applications are missing and as a result need to be created

The System/Data matrix is a two-dimensional table with Logical Application Component on one axis and Data Entity on the other axis.

Class Diagram

The key purpose of the Class diagram is to depict the relationships among the critical data entities (or classes) within the enterprise. This diagram is developed to clearly present the relationships and to help understand the lower-level data models for the enterprise.

Data Dissemination Diagram

The purpose of the Data Dissemination diagram is to show the relationship between data entity, business service, and application components. The diagram shows how the logical entities are to be physically realized by application components. This allows effective sizing to be carried out and the IT footprint to be refined. Moreover, by assigning business value to data, an indication of the business criticality of application components can be gained.

Additionally, the diagram may show data replication and system ownership of the master reference for data. In this instance, it can show two copies and the master-copy relationship between them. This diagram can include services; that is, services encapsulate data and they reside in an application, or services that reside on an application and access data encapsulated within the application.

Data Security Diagram

Data is considered as an asset to the enterprise and data security simply means ensuring that enterprise data is not compromised and that access to it is suitably controlled.

The purpose of the Data Security diagram is to depict which actor (person, organization, or system) can access which enterprise data. This relationship can be shown in a matrix form between two objects or can be shown as a mapping.

The diagram can also be used to demonstrate compliance with data privacy laws and other applicable regulations (HIPAA, SOX, etc). This diagram should also consider any trust implications where an enterprise's partners or other parties may have access to the company's systems, such as an outsourced situation where information may be managed by other people and may even be hosted in a different country.

Class Hierarchy Diagram

The purpose of the Class Hierarchy diagram is to show the technical stakeholders a perspective of the class hierarchy. The advantage of this diagram is that it allows the stakeholders a technical utilization/usage diagram of the data entity. This diagram gives the stakeholders an idea of who is using the data, how, why, and when. A possible variant can be to use this diagram in auditing.

Data Migration Diagram

Data migration is critical when implementing a package or packaged service-based solution. This is particularly true when an existing legacy application is replaced with a package or an enterprise is to be migrated to a larger packages/packaged services footprint. Packages tend to have their own data model and during data migration the legacy application data may need to be transformed prior to loading into the package.

Data migration activities will usually involve the following steps:

• Extract data from source applications (baseline systems)
• Profile source data
• Perform data transformation operations, including data quality processes:
  • Standardize, normalize, de-duplicate source data (data cleansing)
  • Match, merge, and consolidate data from different source(s)
  • Source-to-target mappings
• Load into target applications (target systems)

The purpose of the Data Migration diagram is to show the flow of data from the source to the target applications. The diagram will provide a visual representation of the spread of sources/targets and serve as a tool for data auditing and establishing traceability. This diagram can be elaborated or enhanced as detailed as necessary. For example, the diagram can contain just an overall layout of migration landscape or could go into individual application metadata element level of detail.

Data Lifecycle Diagram

The Data Lifecycle diagram is an essential part of managing business data throughout its lifecycle from conception until disposal within the constraints of the business process.

The data is considered as an entity in its own right, decoupled from business process and activity. Each change in state is represented on the diagram which may include the event or rules that trigger that change in state.

The separation of data from process allows common data requirements to be identified which enables resource sharing to be achieved more effectively.

35.11 Viewpoints in the Phase C Application Architecture

The following catalogs, matrices, and diagrams may be produced in Phase C (Application Architecture):

• Catalogs:
  • Application Portfolio catalog
  • Interface catalog
• Matrices:
  • System/Organization matrix
  • Role/System matrix
  • System/Function matrix
  • Application Interaction matrix
• Core diagrams:
  • Application Communication diagram
  • Application and User Location diagram
  • System Use-Case diagram
• Extension diagrams:
  • Enterprise Manageability diagram
  • Process/System Realization diagram
  • Software Engineering diagram
  • Application Migration diagram
  • Software Distribution diagram

The following describes each of the catalogs, matrices, and diagrams created within Phase C (Application Architecture).

Application Portfolio Catalog

The purpose of this catalog is to identify and maintain a list of all the applications in the enterprise. This list helps to define the horizontal scope of change initiatives that may impact particular kinds of applications. An agreed Application Portfolio allows a standard set of applications to be defined and governed.

The Application Portfolio catalog provides a foundation on which to base the remaining matrices and diagrams. It is typically the start point of the Application Architecture phase.

Existing application registries and repositories - such as SAP's Solution Manager and System Landscape Directory products - also provide input into this catalog from a baseline and target perspective.

The Application Portfolio catalog contains the following metamodel entities:

• Information System Service
• Logical Application Component
• Physical Application Component

Interface Catalog

The purpose of the Interface catalog is to scope and document the interfaces between applications to enable the overall dependencies between applications to be scoped as early as possible.

Systems will create, read, update, and delete data within other systems; this will be achieved by some kind of interface, whether via a batch file that is loaded periodically, a direct connection to another system's database, or via some form of API or web service.

The mapping of the Application Component-Application Component entity relationship is an important step as it enables the following to take place:

• Understand the degree of interaction between applications, identifying those that are central in terms of their dependencies on other systems
• Understand the number and types of interfaces between applications
• Understand the degree of duplication of interfaces between applications
• Identify the potential for simplification of interfaces when considering the target Application Portfolio
• Support the gap analysis and determine whether any of the applications are missing and as a result need to be created

The Interface catalog contains the following metamodel entities:

• Logical Application Component
• Physical Application Component
• Application communicates with application relationship

System/Organization Matrix

The purpose of this matrix is to depict the relationship between systems (i.e., application components) and organizational units within the enterprise.

Business functions are performed by organizational units. Some of the functions and services performed by those organizational units will be supported by IT systems. The mapping of the Application Component-Organization Unit relationship is an important step as it enables the following to take place:

• Assign usage of applications to the organization units that perform business functions
• Understand the application support requirements of the business services and processes carried out by an organization unit
• Support the gap analysis and determine whether any of the applications are missing and as a result need to be created
• Define the application set used by a particular organization unit

The System/Organization matrix is a two-dimensional table with Logical/Physical Application Component on one axis and Organization Unit on the other axis.

The relationship between these two entities is a composite of a number of metamodel relationships that need validating:

• Organization Units own Services
• Actors that belong to Organization Units use Services
• Services are realized by Logical/Physical Application Components

Role/System Matrix

The purpose of the Role/System matrix is to depict the relationship between systems (i.e., application components) and the business roles that use them within the enterprise.

People in an organization interact with systems. During this interaction, these people assume a specific role to perform a task; for example, product buyer.

The mapping of the Application Component-Role relationship is an important step as it enables the following to take place:

• Assign usage of applications to the specific roles in the organization
• Understand the application security requirements of the business services and processes supporting the function, and check these are in line with current policy
• Support the gap analysis and determine whether any of the applications are missing and as a result need to be created
• Define the application set used by a particular business role; essential in any move to role-based computing

The Role/System matrix is a two-dimensional table with Logical Application Component on one axis and Role on the other axis.

The relationship between these two entities is a composite of a number of metamodel relationships that need validating:

• Role accesses Function
• Function is bounded by Service
• Services are realized by Logical/Physical Application Components

System/Function Matrix

The purpose of the System/Function matrix is to depict the relationship between systems (i.e., application components) and business functions within the enterprise.

Business functions are performed by organizational units. Some of the business functions and services will be supported by IT systems. The mapping of the Application Component-Function relationship is an important step as it enables the following to take place:

• Assign usage of applications to the business functions that are supported by them
• Understand the application support requirements of the business services and processes carried out
• Support the gap analysis and determine whether any of the applications are missing and as a result need to be created
• Define the application set used by a particular business function

The System/Organization matrix is a two-dimensional table with Logical Application Component on one axis and Function on the other axis.

The relationship between these two entities is a composite of a number of metamodel relationships that need validating:

• Function is bounded by Service
• Services are realized by Logical/Physical Application Components

Application Interaction Matrix

The purpose of the Application Interaction matrix is to depict communications relationships between systems (i.e., application components).

The mapping of the application interactions shows in matrix form the equivalent of the Interface Catalog or an Application Communication diagram.

The Application Interaction matrix is a two-dimensional table with Application Service, Logical Application Component, and Physical Application Component on both the rows and the columns of the table.

The relationships depicted by this matrix include:

• Application Service consumes Application Service
• Logical Application Component communicates with Logical Application Component
• Physical Application Component communicates with Physical Application Component

Application Communication Diagram

The purpose of the Application Communication diagram is to depict all models and mappings related to communication between applications in the metamodel entity.

It shows application components and interfaces between components. Interfaces may be associated with data entities where appropriate. Applications may be associated with business services where appropriate. Communication should be logical and should only show intermediary technology where it is architecturally relevant.

Application and User Location Diagram

The Application and User Location diagram shows the geographical distribution of applications. It can be used to show where applications are used by the end user; the distribution of where the host application is executed and/or delivered in thin client scenarios; the distribution of where applications are developed, tested, and released; etc.

Analysis can reveal opportunities for rationalization, as well as duplication and/or gaps.

The purpose of this diagram is to clearly depict the business locations from which business users typically interact with the applications, but also the hosting location of the application infrastructure.

The diagram enables:

• Identification of the number of package instances needed to sufficiently support the user population that may be spread out geographically
• Estimation of the number and the type of user licenses for the package or other software
• Estimation of the level of support needed for the users and location of support center
• Selection of system management tools, structure, and management system required to support the enterprise users/customers/partners both locally and remotely
• Appropriate planning for the technological components of the business, namely server sizing and network bandwidth, etc.
• Performance considerations while implementing application and technology architecture solutions

Users typically interact with applications in a variety of ways; for example:

• To support the operations of the business day-to-day
• To participate in the execution of a business process
• To access information (look-up, read)
• To develop the application
• To administer and maintain the application

System Use-Case Diagram

A System Use-Case diagram displays the relationships between consumers and providers of application services. Application services are consumed by actors or other application services and the Application Use-Case diagram provides added richness in describing application functionality by illustrating how and when that functionality is used.

The purpose of the System Use-Case diagram is to help to describe and validate the interaction between actors and their roles with applications. As the architecture progresses, the use-case can evolve from functional information to include technical realization detail.

Architectural system use-cases can also be re-used in more detailed systems design work.

Enterprise Manageability Diagram

The Enterprise Manageability diagram shows how one or more applications interact with application and technology components that support operational management of a solution.

This diagram is really a filter on the Application Communication diagram, specifically for enterprise management class software.

Analysis can reveal duplication and gaps, and opportunities in the IT service management operation of an organization.

Process/System Realization Diagram

The purpose of the Process/System Realization diagram is to clearly depict the sequence of events when multiple applications are involved in executing a business process.

It enhances the Application Communication diagram by augmenting it with any sequencing constraints, and hand-off points between batch and real-time processing.

It would identify complex sequences that could be simplified, and identify possible rationalization points in the architecture in order to provide more timely information to business users. It may also identify process efficiency improvements that may reduce interaction traffic between applications.

Software Engineering Diagram

The Software Engineering diagram breaks applications into packages, modules, services, and operations from a development perspective.

It enables more detailed impact analysis when planning migration stages, and analyzing opportunities and solutions.

It is ideal for application development teams and application management teams when managing complex development environments.

Application Migration Diagram

The Application Migration diagram identifies application migration from baseline to target application components. It enables a more accurate estimation of migration costs by showing precisely which applications and interfaces need to be mapped between migration stages.

It would identify temporary applications, staging areas, and the infrastructure required to support migrations (for example, parallel run environments, etc).

Software Distribution Diagram

The Software Distribution diagram shows how application software is structured and distributed across the estate. It is useful in systems upgrade or application consolidation projects.

This diagram shows how physical applications are distributed across physical technology and the location of that technology.

This enables a clear view of how the software is hosted, but also enables managed operations staff to understand how that application software is maintained once installed.

35.12 Viewpoints in Phase D

The following catalogs, matrices, and diagrams may be produced in Phase D (Technology Architecture).

• Catalogs:
  • Technology Standards catalog
  • Technology Portfolio catalog
• Matrices:
  • System/Technology matrix
• Core diagrams:
  • Environments and Locations diagram
  • Platform Decomposition diagram
• Extension diagrams:
  • Processing diagram
  • Networked Computing/Hardware diagram
  • Communications Engineering diagram

The following section describes each of the catalogs, matrices, and diagrams created within Phase D (Technology Architecture).

Technology Standards Catalog

The Technology Standards catalog documents the agreed standards for technology across the enterprise covering technologies, and versions, the technology lifecycles, and the refresh cycles for the technology.

Depending upon the organization, this may also include location or business domain-specific standards information.

This catalog provides a snapshot of the enterprise standard technologies that are or can be deployed, and also helps identify the discrepancies across the enterprise.

If technology standards are currently in place, apply these to the Technology Portfolio catalog to gain a baseline view of compliance with technology standards.

The Technology Portfolio catalog contains the following metamodel entities:

• Platform Service
• Logical Technology Component
• Physical Technology Component

Technology Portfolio Catalog

The purpose of this catalog is to identify and maintain a list of all the technology in use across the enterprise, including hardware, infrastructure software, and application software. An agreed technology portfolio supports lifecycle management of technology products and versions and also forms the basis for definition of technology standards.

The Technology Portfolio catalog provides a foundation on which to base the remaining matrices and diagrams. It is typically the start point of the Technology Architecture phase.

Technology registries and repositories also provide input into this catalog from a baseline and target perspective.

Technologies in the catalog should be classified against the TOGAF Technology Reference Model (TRM) - see Part VI, 43. Foundation Architecture: Technical Reference Model - extending the model as necessary to fit the classification of technology products in use.

The Technology Portfolio catalog contains the following metamodel entities:

• Platform Service
• Logical Technology Component
• Physical Technology Component

System/Technology Matrix

The System/Technology matrix documents the mapping of business systems to technology platform.

This matrix should be aligned with and complement one or more platform decomposition diagrams.

The System/Technology matrix shows:

• Logical/Physical Application Components
• Services, Logical Technology Components, and Physical Technology Components
• Physical Technology Component realizes Physical Application Component relationships

Environments and Locations Diagram

The Environments and Locations diagram depicts which locations host which applications, identifies what technologies and/or applications are used at which locations, and finally identifies the locations from which business users typically interact with the applications.

This diagram should also show the existence and location of different deployment environments, including non-production environments, such as development and pre production.

Platform Decomposition Diagram

The Platform Decomposition diagram depicts the technology platform that supports the operations of the Information Systems Architecture. The diagram covers all aspects of the infrastructure platform and provides an overview of the enterprise's technology platform. The diagram can be expanded to map the technology platform to appropriate application components within a specific functional or process area. This diagram may show details of specification, such as product versions, number of CPUs, etc. or simply could be an informal "eye-chart" providing an overview of the technical environment.

The diagram should clearly show the enterprise applications and the technology platform for each application area can further be decomposed as follows:

• Hardware:
  • Logical Technology Components (with attributes)
  • Physical Technology Components (with attributes)
• Software:
  • Logical Technology Components (with attributes)
  • Physical Technology Components (with attributes)

Depending upon the scope of the enterprise architecture work, additional technology cross-platform information (e.g., communications, telco, and video information) may be addressed.

Processing Diagram

The Processing diagram focuses on deployable units of code/configuration and how these are deployed onto the technology platform. A deployment unit represents grouping of business function, service, or application components. The Processing diagram addresses the following:

• Which set of application components need to be grouped to form a deployment unit
• How one deployment unit connects/interacts with another (LAN, WAN, and the applicable protocols)
• How application configuration and usage patterns generate load or capacity requirements for different technology components

The organization and grouping of deployment units depends on separation concerns of the presentation, business logic, and data store layers and service-level requirements of the components. For example, presentation layer deployment unit is grouped based on the following:

• Application components that provide UI or user access functions
• Application components that are differentiated by location and user roles

There are several considerations to determine how application components are grouped together. Each deployment unit is made up of sub-units, such as:

• Installation: Part that holds the executable code or package configuration (in case of packages).
• Execution: Application component with its associated state at run time.
• Persistence: Data that represents the persistent state of the application component.

Finally, these deployment units are deployed on either dedicated or shared technology components (workstation, web server, application server, or database server, etc.). It is important to note that technology processing can influence and have implications on the services definition and granularity.

Networked Computing/Hardware Diagram

Starting with the transformation to client-server systems from mainframes and later with the advent of e-Business and J2EE, large enterprises moved predominantly into a highly network-based distributed network computing environment with firewalls and demilitarized zones. Currently, most of the applications have a web front-end and, looking at the deployment architecture of these applications, it is very common to find three distinct layers in the network landscape; namely a web presentation layer, an business logic or application layer, and a back-end data store layer. It is a common practice for applications to be deployed and hosted in a shared and common infrastructure environment.

So it becomes highly critical to document the mapping between logical applications and the technology components (e.g., server) that supports the application both in the development and production environments. The purpose of this diagram is to show the "as deployed" logical view of logical application components in a distributed network computing environment. The diagram is useful for the following reasons:

• Enable understanding of which application is deployed where in the distributed network computing environment
• Establishing authorization, security, and access to these technology components
• Understand the Technology Architecture that support the applications during problem resolution and troubleshooting
• Isolate performance problems encountered by applications, determine whether it is application code-related or technology platform-related, and perform necessary upgrade to specific physical technology components
• Identify areas of optimization as and when newer technologies are available which will eventually reduce cost
• Enable application/technology auditing and prove compliance with enterprise technology standards
• Serve as an important tool to introduce changes to the Technology Architecture, thereby supporting effective change management
• Establish traceability and changing application end-point address while moving application either from a shared environment to a dedicated environment or vice versa

The scope of the diagram can be appropriately defined to cover a specific application, business function, or the entire enterprise. If chosen to be developed at the enterprise level, then the network computing landscape can be depicted in an application agnostic way as well.

Communications Engineering Diagram

The Communications Engineering diagram describes the means of communication - the method of sending and receiving information - between these assets in the Technology Architecture; insofar as the selection of package solutions in the preceding architectures put specific requirements on the communications between the applications.

The Communications Engineering diagram will take logical connections between client and server components and identify network boundaries and network infrastructure required to physically implement those connections. It does not describe the information format or content, but will address protocol and capacity issues.

35.13 Viewpoints in Phase E

The following catalogs, matrices, and diagrams may be produced in Phase E (Opportunities & Solutions).

• Catalogs:
  • No catalogs are defined to be created during Phase E.
• Matrices:
  • No matrices are defined to be created during Phase E.
• Core diagrams:
  • Project Context diagram
  • Benefits diagram
• Extension diagrams:
  • No extension diagrams are defined to be created during Phase E.

The following section describes each of the catalogs, matrices, and diagrams created within Phase E (Opportunities & Solutions).

Project Context Diagram

A Project Context diagram shows the scope of a work package to be implemented as a part of a broader transformation roadmap. The Project Context diagram links a work package to the organizations, functions, services, processes, applications, data, and technology that will be added, removed, or impacted by the project.

The Project Context diagram is also a valuable tool for project portfolio management and project mobilization.

Benefits Diagram

The Benefits diagram shows opportunities identified in an architecture definition, classified according to their relative size, benefit, and complexity. This diagram can be used by stakeholders to make selection, prioritization, and sequencing decisions on identified opportunities.

35.14 Viewpoints for Requirements Management

The following catalogs, matrices, and diagrams may be produced in the Requirements Management phase.

• Catalogs:
  • Requirements catalog
• Matrices:
  • No matrices are defined to be created during the Requirements Management phase.
• Core diagrams:
  • No core diagrams are defined to be created during the Requirements Management phase.
• Extension diagrams:
  • No extension diagrams are defined to be created during the Requirements Management phase.

The following section describes each of the catalogs, matrices, and diagrams created within the Requirements Management phase.

Requirements Catalog

The Requirements catalog captures things that the enterprise needs to do to meet its objectives. Requirements generated from architecture engagements are typically implemented through change initiatives identified and scoped during Phase E (Opportunities & Solutions). Requirements can also be used as a quality assurance tool to ensure that a particular architecture is fit-for-purpose (i.e., can the architecture meet all identified requirements).

The Requirements catalog contains the following metamodel entities:

• Requirement
• Assumption
• Constraint
• Gap

35.15 Developing a Business Architecture View

The Business Architecture view is concerned with addressing the concerns of users.

35.15.1 Stakeholders and Concerns

This view should be developed for the users. It focuses on the functional aspects of the system from the perspective of the users of the system.

Addressing the concerns of the users includes consideration of the following:

People

The human resource aspects of the system. It examines the human actors involved in the system.

Process

Deals with the user processes involved in the system.

Function

Deals with the functions required to support the processes.

Business Information

Deals with the information required to flow in support of the processes.

Usability

Considers the usability aspects of the system and its environment.

Performance

Considers the performance aspects of the system and its environment.

35.15.2 Developing the View

Business scenarios (see Part III, 26. Business Scenarios) are an important technique that may be used prior to, and as a key input to, the development of the Business Architecture view, to help identify and understand business needs, and thereby to derive the business requirements and constraints that the architecture development has to address. Business scenarios are an extremely useful way to depict what should happen when planned and unplanned events occur. It is highly recommended that business scenarios be created for planned change, and for unplanned change.

The following section describe some of the key issues that the architect might consider when constructing business scenarios.

35.15.3 Key Issues

The Business Architecture view considers the functional aspects of the system; that is, what the new system is intended to do. This can be built up from an analysis of the existing environment and of the requirements and constraints affecting the new system.

The new requirements and constraints will appear from a number of sources, possibly including:

• Existing internal specifications and lists of approved products
• Business goals and objectives
• Business process re-engineering activities
• Changes in technology

What should emerge from the Business Architecture view is a clear understanding of the functional requirements for the new architecture, with statements like: "Improvements in handling customer enquiries are required through wider use of computer/telephony integration".

The Business Architecture view considers the usability aspects of the system and its environment. It should also consider impacts on the user such as skill levels required, the need for specialized training, and migration from current practice. When considering usability the architect should take into account:

• The ease-of-use of the user interface, and how intuitive it is
• Whether or not there is transparent access to data and applications, irrespective of location
• Ease-of-management of the user environment by the user
• Application interoperability through means such as drag-and-drop
• Online help facilities
• Clarity of documentation
• Security and password aspects, such as avoiding the requirement for multiple sign-on and password dialogs
• Access to productivity applications, such as mail or a spreadsheet

Note that, although security and management are thought about here, it is from a usability and functionality point of view. The technical aspects of security and management are considered in the Enterprise Security view (see 35.16 Developing an Enterprise Security View) and the Enterprise Manageability view (see 35.21 Developing an Enterprise Manageability View).

35.16 Developing an Enterprise Security View

The Enterprise Security view is concerned with the security aspects of the system.

35.16.1 Stakeholders and Concerns

This view should be developed for security engineers of the system. It focuses on how the system is implemented from the perspective of security, and how security affects the system properties. It examines the system to establish what information is stored and processed, how valuable it is, what threats exist, and how they can be addressed.

Major concerns for this view are understanding how to ensure that the system is available to only those that have permission, and how to protect the system from unauthorized tampering.

35.16.2 Developing the View

The subjects of the general architecture of a "security system" are components that are secured, or components that provide security services. Additionally Access Control Lists (ACLs) and security schema definitions are used to model and implement security.

35.16.3 Basic Concepts

This section presents basic concepts required for an understanding of information system security.

The essence of security is the controlled use of information. The purpose of this section is to provide a brief overview of how security protection is implemented in the components of an information system. Doctrinal or procedural mechanisms, such as physical and personnel security procedures and policy, are not discussed here in any depth.

Abstract Security Architecture View depicts an abstract view of an Information Systems Architecture, which emphasizes the fact that an information system from the security perspective is either part of a Local Subscriber Environment (LSE) or a Communications Network (CN). An LSE may be either fixed or mobile. The LSEs by definition are under the control of the using organization. In an open system distributed computing implementation, secure and non-secure LSEs will almost certainly be required to interoperate.

35.16.3.1 Information Domains

The concept of an information domain provides the basis for discussing security protection requirements. An information domain is defined as a set of users, their information objects, and a security policy. An information domain security policy is the statement of the criteria for membership in the information domain and the required protection of the information objects. Breaking an organization's information down into domains is the first step in reducing the task of security policy development to a manageable size.

The business of most organizations requires that their members operate in more than one information domain. The diversity of business activities and the variation in perception of threats to the security of information will result in the existence of different information domains within one organization security policy. A specific activity may use several information domains, each with its own distinct information domain security policy.

Information domains are not necessarily bounded by information systems or even networks of systems. The security mechanisms implemented in information system components may be evaluated for their ability to meet the information domain security policies.

35.16.3.2 Strict Isolation

Information domains can be viewed as being strictly isolated from one another. Information objects should be transferred between two information domains only in accordance with established rules, conditions, and procedures expressed in the security policy of each information domain.

35.16.3.3 Absolute Protection

The concept of "absolute protection" is used to achieve the same level of protection in all information systems supporting a particular information domain. It draws attention to the problems created by interconnecting LSEs that provide different strengths of security protection. This interconnection is likely because open systems may consist of an unknown number of heterogeneous LSEs. Analysis of minimum security requirements will ensure that the concept of absolute protection will be achieved for each information domain across LSEs.

35.16.4 Security Generic Architecture View

Generic Security Architecture View shows a generic architecture view which can be used to discuss the allocation of security services and the implementation of security mechanisms. This view identifies the architectural components within an LSE. The LSEs are connected by CNs. The LSEs include end systems, relay systems, and Local Communications Systems (LCSs), described below.

• Relay System (RS): The component of an LSE, the functionality of which is limited to information transfer and is only indirectly accessible by users (e.g., router, switch, multiplexor, Message Transfer Agent (MTA)). It may have functionality similar to an end system, but an end user does not use it directly. Note that relay system functions may be provided in an end system.
• Local Communication System (LCS): A network that provides communications capabilities between LSEs or within an LSE with all of the components under control of an LSE.
• Communications Network (CN): A network that provides inter-LSE communications capabilities, but is not controlled by LSEs (e.g., commercial carriers).

The end system and the relay system are viewed as requiring the same types of security protection. For this reason, a discussion of security protection in an end system generally also applies to a relay system. The security protections in an end system could occur in both the hardware and software.

35.16.5 Security Services Allocation

Security protection of an information system is provided by mechanisms implemented in the hardware and software of the system and by the use of doctrinal mechanisms. The mechanisms implemented in the system hardware and software are concentrated in the end system or relay system. This focus for security protection is based on the open system, distributed computing approach for information systems. This implies use of commercial common carriers and private common-user communications systems as the CN provider between LSEs. Thus, for operation of end systems in a distributed environment, a greater degree of security protection can be ensured from implementation of mechanisms in the end system or relay system.

However, communications networks should satisfy the availability element of security in order to provide appropriate security protection for the information system. This means that CNs must provide an agreed level of responsiveness, continuity of service, and resistance to accidental and intentional threats to the communications service availability.

Implementing the necessary security protection in the end system occurs in three system service areas of TOGAF. They are operating system services, network services, and system management services.

Most of the implementation of security protection is expected to occur in software. The hardware is expected to protect the integrity of the end-system software. Hardware security mechanisms include protection against tampering, undesired emanations, and cryptography.

35.16.5.1 Operating System Services

A "security context" is defined as a controlled process space subject to an information domain security policy. The security context is therefore analogous to a common operating system notion of user process space. Isolation of security contexts is required. Security contexts are required for all applications (e.g., end-user and security management applications). The focus is on strict isolation of information domains, management of end-system resources, and controlled sharing and transfer of information among information domains. Where possible, security-critical functions should be isolated into relatively small modules that are related in well-defined ways.

The operating system will isolate multiple security contexts from each other using hardware protection features (e.g., processor state register, memory mapping registers) to create separate address spaces for each of them. Untrusted software will use end-system resources only by invoking security-critical functions through the separation kernel. Most of the security-critical functions are the low-level functions of traditional operating systems.

35.16.5.2 Network Services

Two basic classes of communications are envisioned for which distributed security contexts may need to be established. These are interactive and staged (store and forward) communications.

The concept of a "security association" forms an interactive distributed security context. A security association is defined as all the communication and security mechanisms and functions that extend the protections required by an information domain security policy within an end system to information in transfer between multiple end systems. The security association is an extension or expansion of an OSI application layer association. An application layer association is composed of appropriate application layer functions and protocols plus all of the underlying communications functions and protocols at other layers of the OSI model. Multiple security protocols may be included in a single security association to provide for a combination of security services.

For staged delivery communications (e.g., email), use will be made of an encapsulation technique (termed "wrapping process") to convey the necessary security attributes with the data being transferred as part of the network services. The wrapped security attributes are intended to permit the receiving end system to establish the necessary security context for processing the transferred data. If the wrapping process cannot provide all the necessary security protection, interactive security contexts between end systems will have to be used to ensure the secure staged transfer of information.

35.16.5.3 System Security Management Services

Security management is a particular instance of the general information system management functions discussed in earlier chapters. Information system security management services are concerned with the installation, maintenance, and enforcement of information domain and information system security policy rules in the information system intended to provide these security services. In particular, the security management function controls information needed by operating system services within the end system security architecture. In addition to these core services, security management requires event handling, auditing, and recovery. Standardization of security management functions, data structures, and protocols will enable interoperation of Security Management Application Processes (SMAPs) across many platforms in support of distributed security management.

35.17 Developing a Software Engineering View

The Software Engineering view is concerned with the development of new software systems.

35.17.1 Stakeholders and Concerns

Building a software-intensive system is both expensive and time-consuming. Because of this, it is necessary to establish guidelines to help minimize the effort required and the risks involved. This is the purpose of the Software Engineering view, which should be developed for the software engineers who are going to develop the system.

Major concerns for these stakeholders are:

• Development approach
• Software modularity and re-use
• Portability
• Migration and interoperability

35.17.1.1 Development Approach

There are many lifecycle models defined for software development (waterfall, prototyping, etc.). A consideration for the architect is how best to feed architectural decisions into the lifecycle model that is going to be used for development of the system.

35.17.1.2 Software Modularity and Re-Use

As a piece of software grows in size, so the complexity and inter-dependencies between different parts of the code increase. Reliability will fall dramatically unless this complexity can be brought under control.

Modularity is a concept by which a piece of software is grouped into a number of distinct and logically cohesive sub-units, presenting services to the outside world through a well-defined interface. Generally speaking, the components of a module will share access to common data, and the interface will provide controlled access to this data. Using modularity, it becomes possible to build a software application incrementally on a reliable base of pre-tested code.

A further benefit of a well-defined modular system is that the modules defined within it may be re-used in the same or on other projects, cutting development time dramatically by reducing both development and testing effort.

In recent years, the development of object-oriented programming languages has greatly increased programming language support for module development and code re-use. Such languages allow the developer to define "classes" (a unit of modularity) of objects that behave in a controlled and well-defined manner. Techniques such as inheritance - which enables parts of an existing interface to an object to be changed - enhance the potential for re-usability by allowing predefined classes to be tailored or extended when the services they offer do not quite meet the requirement of the developer.

If modularity and software re-use are likely to be key objectives of new software developments, consideration must be given to whether the component parts of any proposed architecture may facilitate or prohibit the desired level of modularity in the appropriate areas.

35.17.1.3 Portability

Software portability - the ability to take a piece of software written in one environment and make it run in another - is important in many projects, especially product developments. It requires that all software and hardware aspects of a chosen Technology Architecture (not just the newly developed application) be available on the new platform. It will, therefore, be necessary to ensure that the component parts of any chosen architecture are available across all the appropriate target platforms.

35.17.1.4 Migration and Interoperability

Interoperability is always required between the component parts of a new architecture. It may also, however, be required between a new architecture and parts of an existing legacy system; for example, during the staggered replacement of an old system. Interoperability between the new and old architectures may, therefore, be a factor in architectural choice.

35.17.2 Key Issues

• Data-intensive versus information-intensive software systems
• Achieving interoperability
• Software tiers
• Uses of a data access tier
• Distribution

35.17.2.1 Data-Intensive versus Information-Intensive Software Systems

This view considers two general categories of software systems. First, there are those systems that require only a user interface to a database, requiring little or no business logic built into the software. These systems can be called "data-intensive". Second, there are those systems that require users to manipulate information that might be distributed across multiple databases, and to do this manipulation according to a predefined business logic. These systems can be called "information-intensive"

Data-intensive systems can be built with reasonable ease through the use of 4GL tools. In these systems, the business logic is in the mind of the user; i.e., the user understands the rules for manipulating the data and uses those rules while doing his work.

Information-intensive systems are different. Information is defined as "meaningful data"; i.e., data in a context that includes business logic. Information is different from data. Data is the tokens that are stored in databases or other data stores. Information is multiple tokens of data combined to convey a message. For example, "3" is data, but "3 widgets" is information. Typically, information reflects a model. Information-intensive systems also tend to require information from other systems and, if this path of information passing is automated, usually some mediation is required to convert the format of incoming information into a format that can be locally used. Because of this, information-intensive systems tend to be more complex than others, and require the most effort to build, integrate, and maintain.

This view is concerned primarily with information-intensive systems. In addition to building systems that can manage information, though, systems should also be as flexible as possible. This has a number of benefits. It allows the system to be used in different environments; for example, the same system should be usable with different sources of data, even if the new data store is a different configuration. Similarly, it might make sense to use the same functionality but with users who need a different user interface. So information systems should be built so that they can be reconfigured with different data stores or different user interfaces. If a system is built to allow this, it enables the enterprise to re-use parts (or components) of one system in another.

35.17.2.2 Achieving Interoperability

The word "interoperate" implies that one processing system performs an operation on behalf of or at the behest of another processing system. In practice, the request is a complete sentence containing a verb (operation) and one or more nouns (identities of resources, where the resources can be information, data, physical devices, etc.). Interoperability comes from shared functionality.

Interoperability can only be achieved when information is passed, not when data is passed. Most information systems today get information both from their own data stores and other information systems. In some cases the web of connectivity between information systems is quite extensive. The US Air Force, for example, has a concept known as "A5 Interoperability". This means that the required data is available Anytime, Anywhere, by Anyone, who is Authorized, in Any way. This requires that many information systems are architecturally linked and provide information to each other.

There must be some kind of physical connectivity between the systems. This might be a Local Area Network (LAN), a Wide Area Network (WAN), or, in some cases, it might simply be the passing data storage media between systems. Assuming a network connects the systems, there must be agreement on the protocols used. This enables the transfer of bits.

When the bits are assembled at the receiving system, they must be placed in the context that the receiving system needs. In other words, both the source and destination systems must agree on an information model. The source system uses this model to convert its information into data to be passed, and the destination system uses this same model to convert the received data into information it can use.

This usually requires an agreement between the architects and designers of the two systems. In the past, this agreement was often documented in the form of an Interface Control Document (ICD). The ICD defines the exact syntax and semantics that the sending system will use so that the receiving system will know what to do when the data arrives. The biggest problem with ICDs is that they tend to be unique solutions between two systems. If a given system must share information with n other systems, there is the potential need for n2 ICDs. This extremely tight integration prohibits flexibility and the ability of a system to adapt to a changing environment. Maintaining all these ICDs is also a challenge.

New technology, such as eXtensible Markup Language (XML), has the promise of making data "self describing". Use of new technologies such as XML, once they become reliable and well documented, might eliminate the need for an ICD. Further, there would be Commercial Off-The-Shelf (COTS) products available to parse and manipulate the XML data, eliminating the need to develop these products in-house. It should also ease the pain of maintaining all the interfaces.

Another approach is to build "mediators" between the systems. Mediators would use metadata that is sent with the data to understand the syntax and semantics of the data and convert it into a format usable by the receiving system. However, mediators do require that well-formed metadata be sent, adding to the complexity of the interface.

35.17.2.3 Software Tiers

Typically, software architectures are either two-tier or three-tier.²

Each tier typically presents at least one capability.

Two-Tier

In a two-tier architecture, the user interface and business logic are tightly coupled while the data is kept independent. This gives the advantage of allowing the data to reside on a dedicated data server. It also allows the data to be independently maintained. The tight coupling of the user interface and business logic ensure that they will work well together, for this problem in this domain. However, the tight coupling of the user interface and business logic dramatically increases maintainability risks while reducing flexibility and opportunities for re-use.

Three-Tier

A three-tier approach adds a tier that separates the business logic from the user interface. This in principle allows the business logic to be used with different user interfaces as well as with different data stores. With respect to the use of different user interfaces, users might want the same user interface but using different COTS presentation servers; for example, Java Virtual Machine (JVM). Similarly, if the business logic is to be used with different data stores, then each data store must use the same data model³ (data standardization), or a mediation tier must be added above the data store (data encapsulation).

Five-Tier

To achieve maximum flexibility, software should utilize a five-tier scheme for software which extends the three-tier paradigm (see The Five-Tier Organization). The scheme is intended to provide strong separation of the three major functional areas of the architecture. Since there are client and server aspects of both the user interface and the data store, the scheme then has five tiers.⁴

The presentation tier is typically COTS-based. The presentation interface might be an X Server, Win32, etc. There should be a separate tier for the user interface client. This client establishes the look-and-feel of the interface; the server (presentation tier) actually performs the tasks by manipulating the display. The user interface client hides the presentation server from the application business logic.

The application business logic (e.g., a scheduling engine) should be a separate tier. This tier is called the "application logic" and functions as a server for the user interface client. It interfaces to the user interface typically through callbacks. The application logic tier also functions as a client to the data access tier.

If there is a user need to use an application with multiple databases with different schema, then a separate tier is needed for data access. This client would access the data stores using the appropriate COTS interface⁵ and then convert the raw data into an abstract data type representing parts of the information model. The interface into this object network would then provide a generalized Data Access Interface (DAI) which would hide the storage details of the data from any application that uses that data.

Each tier in this scheme can have zero or more components. The organization of the components within a tier is flexible and can reflect a number of different architectures based on need. For example, there might be many different components in the application logic tier (scheduling, accounting, inventory control, etc.) and the relationship between them can reflect whatever architecture makes sense, but none of them should be a client to the presentation server.

This clean separation of user interface, business logic, and information will result in maximum flexibility and componentized software that lends itself to product line development practices. For example, it is conceivable that the same functionality should be built once and yet be usable by different presentation servers (e.g., on PCs or UNIX system boxes), displayed with different looks and feels depending on user needs, and usable with multiple legacy databases. Moreover, this flexibility should not require massive rewrites to the software whenever a change is needed.

35.17.2.4 Some Uses of a Data Access Tier

The data access tier provides a standardized view of certain classes of data, and as such functions as a server to one or more application logic tiers. If implemented correctly, there would be no need for application code to "know" about the implementation details of the data. The application code would only have to know about an interface that presents a level of abstraction higher than the data. This interface is called the Data Access Interface (DAI).

For example, should a scheduling engine need to know what events are scheduled between two dates, that query should not require knowledge of tables and joins in a relational database. Moreover, the DAI could provide standardized access techniques for the data. For example, the DAI could provide a Publish and Subscribe (P&S) interface whereby systems which require access to data stores could register an interest in certain types of data, perhaps under certain conditions, and the DAI would provide the required data when those conditions occur.

35.17.2.5 One Possible Instantiation of a DAI

One means to instantiate a data access component is with three layers, as shown in Data Access Interface (DAI) . This is not the only means to build a DAI, but is presented as a possibility.

Whereas the Direct Data Access layer contains the implementation details of one or more specific data stores, the Object Network and the Information Distribution layer require no such knowledge. Instead, the upper two layers reflect the need to standardize the interface for a particular domain. The Direct Data Access layer spans the gap between the Data Access tier and the Data Store tier, and therefore has knowledge of the implementation details of the data. SQL statements, either embedded or via a standard such as DRDA or ODBC, are located here.

The Object Network layer is the instantiation in software of the information model. As such, it is an efficient means to show the relationships that hold between pieces of data. The translation of data accesses to objects in the network would be the role of the Direct Data Access layer.

Within the Information Distribution layer lies the interface to the "outside world". This interface typically uses a data bus to distribute the data (see below).⁶ It could also contain various information-related services; for example, a P&S registry and publication service or an interface to a security server for data access control.⁷ The Information Distribution layer might also be used to distribute applications or applets required to process distributed information. Objects in the object network would point to the applications or applets, allowing easy access to required processing code.

35.17.2.6 DAIs Enable Flexibility

The DAI enables a very flexible architecture. Multiple raw capabilities can access the same or different data stores, all through the same DAI. Each DAI might be implemented in many ways, according to the specific needs of the raw capabilities using it. Multiple Uses of a Data Access Interface (DAI) illustrates a number of possibilities, including multiple different DAIs in different domains accessing the same database, a single DAI accessing multiple databases, and multiple instantiations of the same DAI access the same database.

It is not always clear that a DAI is needed, and it appears to require additional work during all phases of development. However, should a database ever be redesigned, or if an application is to be re-used and there is no control over how the new data is implemented, using a DAI saves time in the long run.

35.17.2.7 Distribution

The ISO Reference Model for Open Distributed Processing (RM-ODP) offers a meta-standard that is intended to allow more specific standards to emerge. The RM-ODP Reference Model defines a set of distribution transparencies that are applicable to the TOGAF Software Engineering view.

• Access Transparency masks differences in data representation and invocation mechanisms to enable interworking between objects. This transparency solves many of the problems of interworking between heterogeneous systems, and will generally be provided by default.
• Failure Transparency masks from an object the failure and possible recovery of other objects (or itself) to enable fault tolerance. When this transparency is provided, the designer can work in an idealized world in which the corresponding class of failures does not occur.
• Location Transparency masks the use of information about location in space when identifying and binding to interfaces. This transparency provides a logical view of naming, independent of actual physical location.
• Migration Transparency masks from an object the ability of a system to change the location of that object. Migration is often used to achieve load balancing and reduce latency.
• Relocation Transparency masks relocation of an interface from other interfaces bound to it. Relocation allows system operation to continue even when migration or replacement of some objects creates temporary inconsistencies in the view seen by their users.
• Replication Transparency masks the use of a group of mutually behaviorally compatible objects to support an interface. Replication is often used to enhance performance and availability.
• Transaction Transparency masks co-ordination of activities amongst a configuration of objects to achieve consistency.

35.17.2.8 Infrastructure Bus

The infrastructure bus represents the middleware that establishes the client/server relationship. This commercial software is like a backplane onto which capabilities can be plugged. A system should adhere to a commercial implementation of a middleware standard. This is to ensure that capabilities using different commercial implementations of the standard can interoperate. If more than one commercial standard is used (e.g., COM and CORBA), then the system should allow for interoperability between implementations of these standards via the use of commercial bridging software.⁸ Wherever practical, the interfaces should be specified in the appropriate Interface Description Language (IDL). Taken this way, every interface in the five-tier scheme represents an opportunity for distribution.

Clients can interact with servers via the infrastructure bus. In this interaction, the actual network transport (TCP/IP, HTTP, etc.), the platform/vendor of the server, and the operating system of the server are all transparent.

35.17.3 Conclusion

The Software Engineering view gives guidance on how to structure software in a very flexible manner. By following these guidelines, the resulting software will be componentized. This enables the re-use of components in different environments. Moreover, through the use of an infrastructure bus and clean interfaces, the resulting software will be location-independent, enabling its distribution across a network.

35.18 Developing a System Engineering View

The System Engineering view is concerned with assembling software and hardware components into a working system.

35.18.1 Stakeholders and Concerns

This view should be developed for the systems engineering personnel of the system, and should focus on how the system is implemented from the perspective of hardware/software and networking.

Systems engineers are typically concerned with location, modifiability, re-usability, and availability of all components of the system. The System Engineering view presents a number of different ways in which software and hardware components can be assembled into a working system. To a great extent, the choice of model determines the properties of the final system. It looks at technology which already exists in the organization, and what is available currently or in the near future. This reveals areas where new technology can contribute to the function or efficiency of the new architecture, and how different types of processing platform can support different parts of the overall system.

Major concerns for this view are understanding the system requirements. In general these stakeholders are concerned with ensuring that the appropriate components are developed and deployed within the system in an optimal manner.

Developing this view assists in the selection of the best configurations for the system.

35.18.2 Key Issues

This view of the architecture focuses on computing models that are appropriate for a distributed computing environment. To support the migration of legacy systems, this section also presents models that are appropriate for a centralized environment. The definitions of many of the computing models (e.g., host-based, master/slave, and three-tiered) historically preceded the definition of the client/server model, which attempts to be a general-purpose model. In most cases the models have not been redefined in the computing literature in terms of contrasts with the client/server model. Therefore, some of the distinctions of features are not always clean. In general, however, the models are distinguished by the allocation of functions for an information system application to various components (e.g., terminals, computer platforms). These functions that make up an information system application are presentation, application function, and data management.

35.18.2.1 Client/Server Model

Client/server processing is a special type of distributed computing termed "co-operative processing" because the clients and servers co-operate in the processing of a total application (presentation, functional processing, data management). In the model, clients are processes that request services, and servers are processes that provide services. Clients and servers can be located on the same processor, different multi-processor nodes, or on separate processors at remote locations. The client typically initiates communications with the server. The server typically does not initiate a request with a client. A server may support many clients and may act as a client to another server. Basic Client/Server Model depicts a basic client/server model, which emphasizes the request-reply relationships. Reference Model Representation of Client/Server Model shows the same model drawn following the TOGAF TRM, showing how the various entities and interfaces can be used to support a client/server model, whether the server is local or remote to the client. In these representations, the request-reply relationships would be defined in the API.

Clients tend to be generalized and can run on one of many nodes. Servers tend to be specialized and run on a few nodes. Clients are typically implemented as a call to a routine. Servers are typically implemented as a continuous process waiting for service requests (from clients). Many client/server implementations involve remote communications across a network. However, nothing in the client/server model dictates remote communications, and the physical location of clients is usually transparent to the server. The communication between a client and a server may involve a local communication between two independent processes on the same machine.

An application program can be considered to consist of three parts:

• Data handling
• Application function
• Presentation

In general, each of these can be assigned to either a client or server application, making appropriate use of platform services. This assignment defines a specific client/server configuration.

35.18.2.2 Master/Slave and Hierarchic Models

In this model, slave computers are attached to a master computer. In terms of distribution, the master/slave model is one step up from the host-based model. Distribution is provided in one direction - from the master to the slaves. The slave computers perform application processing only when directed to by the master computer. In addition, slave processors can perform limited local processing, such as editing, function key processing, and field validation. A typical configuration might be a mainframe as the master with PCs as the slaves acting as intelligent terminals, as illustrated in Host-Based, Master/Slave, and Hierarchic Models .

The hierarchic model is an extension of the master/slave model with more distribution capabilities. In this approach, the top layer is usually a powerful mainframe, which acts as a server to the second tier. The second layer consists of LAN servers and clients to the first layer as well as servers to the third layer. The third layer consists of PCs and workstations. This model has been described as adding true distributed processing to the master/slave model. Host-Based, Master/Slave, and Hierarchic Models shows an example hierarchic model in the third configuration, and below, Hierarchic Model using the Reference Model shows the hierarchic model represented in terms of the entities and interfaces of the TRM.

35.18.2.3 Peer-to-Peer Model

In the peer-to-peer model there are co-ordinating processes. All of the computers are servers in that they can receive requests for services and respond to them; and all of the computers are clients in that they can send requests for services to other computers. In current implementations, there are often redundant functions on the participating platforms.

Attempts have been made to implement the model for distributed heterogeneous (or federated) database systems. This model could be considered a special case of the client/server model, in which all platforms are both servers and clients. Peer-to-Peer and Distributed Object Management Models (A) shows an example peer-to-peer configuration in which all platforms have complete functions.

35.18.2.4 Distributed Object Management Model

In this model the remote procedure calls typically used for communication in the client/server and other distributed processing models are replaced by messages sent to objects. The services provided by systems on a network are treated as objects. A requester need not know the details of how the object is configured. The approach requires:

• A mechanism to dispatch messages
• A mechanism to co-ordinate delivery of messages
• Applications and services that support a messaging interface

This approach does not contrast with client/server or peer-to-peer models but specifies a consistent interface for communicating between co-operating platforms. It is considered by some as an implementation approach for client/server and peer-to-peer models. Peer-to-Peer and Distributed Object Management Models presents two distributed object model examples. Example B shows how a client/server configuration would be altered to accommodate the distributed object management model. Example C shows how a peer-to-peer model would be altered to accomplish distributed object management.

The Object Management Group (OMG), a consortium of industry participants working toward object standards, has developed an architecture - the Common Object Request Broker Architecture (CORBA) - which specifies the protocol a client application must use to communicate with an Object Request Broker (ORB), which provides services. The ORB specifies how objects can transparently make requests and receive responses. In addition, Microsoft's Object Linking and Embedding (OLE) standard for Windows is an example of an implementation of distributed object management, whereby any OLE-compatible application can work with data from any other OLE-compatible application.

35.19 Developing a Communications Engineering View

The Communications Engineering view is concerned with structuring communications and networking elements to simplify network planning and design.

35.19.1 Stakeholders and Concerns

This view should be developed for the communications engineering personnel of the system, and should focus on how the system is implemented from the perspective of the communications engineer.

Communications engineers are typically concerned with location, modifiability, re-usability, and availability of communications and networking services. Major concerns for this view are understanding the network and communications requirements. In general these stakeholders are concerned with ensuring that the appropriate communications and networking services are developed and deployed within the system in an optimal manner.

Developing this view assists in the selection of the best model of communications for the system.

35.19.2 Key Issues

Communications networks are constructed of end devices (e.g., printers), processing nodes, communication nodes (switching elements), and the linking media that connect them. The communications network provides the means by which information is exchanged. Forms of information include data, imagery, voice, and video. Because automated information systems accept and process information using digital data formats rather than analog formats, the TOGAF communications concepts and guidance will focus on digital networks and digital services. Integrated multimedia services are included.

The Communications Engineering view describes the communications architecture with respect to geography, discusses the Open Systems Interconnection (OSI) reference model, and describes a general framework intended to permit effective system analysis and planning.

35.19.2.1 Communications Infrastructure

The Communications Infrastructure may contain up to three levels of transport - local, regional/metropolitan, and global - as shown in Communications Infrastructure . The names of the transport components are based on their respective geographic extent, but there is also a hierarchical relationship among them. The transport components correspond to a network management structure in which management and control of network resources are distributed across the different levels.

The local components relate to assets that are located relatively close together geographically. This component contains fixed communications equipment and small units of mobile communications equipment. LANs, to which the majority of end devices will be connected, are included in this component. Standard interfaces will facilitate portability, flexibility, and interoperability of LANs and end devices.

Regional and Metropolitan Area Networks (MANs) are geographically dispersed over a large area. A regional or metropolitan network could connect local components at several fixed bases or connect separate remote outposts. In most cases, regional and metropolitan networks are used to connect local networks. However, shared databases, regional processing platforms, and network management centers may connect directly or through a LAN. Standard interfaces will be provided to connect local networks and end devices.

Global or Wide Area Networks (WANs) are located throughout the world, providing connectivity for regional and metropolitan networks in the fixed and deployed environment. In addition, mobile units, shared databases, and central processing centers can connect directly to the global network as required. Standard interfaces will be provided to connect regional and metropolitan networks and end devices.

35.19.2.2 Communications Models

The geographically divided infrastructure described above forms the foundation for an overall communications framework. These geographic divisions permit the separate application of different management responsibilities, planning efforts, operational functions, and enabling technologies to be applied within each area. Hardware and software components and services fitted to the framework form the complete model.

The following sections describe the OSI Reference Model and a grouping of the OSI layers that facilitates discussion of interoperability issues.

The OSI Reference Model

The Open Systems Interconnection (OSI) Reference Model, portrayed in OSI Reference Model , is the model used for data communications in TOGAF. Each of the seven layers in the model represents one or more services or protocols (a set of rules governing communications between systems), which define the functional operation of the communications between user and network elements. Each layer (with the exception of the top layer) provides services for the layer above it. This model aims at establishing open systems operation and implies standards-based implementation. It strives to permit different systems to accomplish complete interoperability and quality of operation throughout the network.

The seven layers of the OSI model are structured to facilitate independent development within each layer and to provide for changes independent of other layers. Stable international standard protocols in conformance with the OSI Reference Model layer definitions have been published by various standards organizations. This is not to say that the only protocols which fit into TOGAF are OSI protocols. Other protocol standards such as SNA or TCP/IP can be described using the OSI seven layer model as a reference.

Support and business area applications, as defined in TOGAF, are above the OSI Reference Model protocol stack and use its services via the applications layer.

Communications Framework

A communications system based on the OSI Reference Model includes services in all the relevant layers, the support and business area application software which sits above the application layer of the OSI Reference Model, and the physical equipment carrying the data. These elements may be grouped into architectural levels that represent major functional capabilities, such as switching and routing, data transfer, and the performance of applications.

These architectural levels are:

• The Transmission level (below the physical layer of the OSI Reference Model) provides all of the physical and electronic capabilities, which establish a transmission path between functional system elements (wires, leased circuits, interconnects, etc.).
• The Network Switching level (OSI layers 1 through 3) establishes connectivity through the network elements to support the routing and control of traffic (switches, controllers, network software, etc.).
• The Data Exchange level (OSI layers 4 through 7) accomplishes the transfer of information after the network has been established (end-to-end, user-to-user transfer) involving more capable processing elements (hosts, workstations, servers, etc.).

  In the TRM, OSI application layer services are considered to be part of the application platform entity, since they offer standardized interfaces to the application programming entity.

• The Applications Program level (above the OSI) includes the support and business area applications (non-management application programs).

The communications framework is defined to consist of the three geographical components of the Communications Infrastructure (local, regional, and global) and the four architectural levels (Transmission, Network Switching, Data Exchange, and Applications Program), and is depicted in Communications Framework . Communications services are performed at one or more of these architectural levels within the geographical components. Communications Framework shows computing elements (operating at the Applications Program level) with supporting data exchange elements, linked with each other through various switching elements (operating at the Network Switching level), each located within its respective geographical component. Communications Framework also identifies the relationship of TOGAF to the communication architecture.

Allocation of Services to Components

The Communications Infrastructure consists of the local, regional, and global transport components. The services allocated to these components are identical to the services of the Application Program, Data Exchange, Network Switching, or Transmission architectural levels that apply to a component. Data Exchange and Network Switching level services are identical to the services of the corresponding OSI Reference Model layers. Typically, only Network Switching and Transmission services are allocated to the regional and global components, which consist of communications nodes and transmission media. All services may be performed in the local component, which includes end devices, processing nodes, communications nodes, and linking media. Transmission, switching, transport, and applications are all performed in this component.

35.20 Developing a Data Flow View

The Data Flow view is concerned with storage, retrieval, processing, archiving, and security of data.

35.20.1 Stakeholders and Concerns

This view should be developed for database engineers of the system.

Major concerns for this view are understanding how to provide data to the right people and applications with the right interfaces at the right time. This view deals with the architecture of the storage, retrieval, processing, archiving, and security of data. It looks at the flow of data as it is stored and processed, and at what components will be required to support and manage both storage and processing. In general, these stakeholders are concerned with ensuring ubiquitous access to high quality data.

35.20.2 Developing the View

The subjects of the general architecture of a "database system" are database components or components that provide database services.

The modeling of a "database" is typically done with entity-relationship diagrams and schema definitions, including document type definitions.

35.20.3 Key Issues

Data management services may be provided by a wide range of implementations. Some examples are:

• Mega-centers providing functionally-oriented corporate databases supporting local and remote data requirements
• Distributed DBMSs that support the interactive use of partitioned and partially replicated databases
• File systems provided by operating systems, which may be used by both interactive and batch processing applications

Data management services include the storage, retrieval, manipulation, backup, restart/recovery, security, and associated functions for text, numeric data, and complex data such as documents, graphics, images, audio, and video. The operating system provides file management services, but they are considered here because many legacy databases exist as one or more files without the services provided by a DBMS.

Major components that provide data management services that are discussed in this section are:

• Database Management Systems (see 35.20.3.1 Database Management Systems)
• Data Dictionary/Directory Systems (see 35.20.3.2 Data Dictionary/Directory Systems)
• Data Administration (see 35.20.3.3 Data Administration)
• Data Security (see 35.20.3.4 Data Security)

These are critical aspects of data management for the following reasons. The DBMS is the most critical component of any data management capability, and a data dictionary/directory system is necessary in conjunction with the DBMS as a tool to aid the administration of the database. Data security is a necessary part of any overall policy for security in information processing.

35.20.3.1 Database Management Systems

A Database Management System (DBMS) provides for the systematic management of data. This data management component provides services and capabilities for defining the data, structuring the data, accessing the data, as well as security and recovery of the data. A DBMS performs the following functions:

• Structures data in a consistent way
• Provides access to the data
• Minimizes duplication
• Allows reorganization; that is, changes in data content, structure, and size
• Supports programming interfaces
• Provides security and control

A DBMS must provide:

• Persistence; the data continues to exist after the application's execution has completed
• Secondary storage management
• Concurrency
• Recovery
• Data Definition/Data Manipulation Language (DDL/DML), which may be a graphical interface

Database Models

The logical data model that underlies the database characterizes a DBMS. The common logical data models are as follows:

• Relational Model: A Relational Database Management System (RDBMS) structures data into tables that have certain properties:
  • Each row in the table is distinct from every other row.
  • Each row contains only atomic data; that is, there is no repeating data or such structures as arrays.
  • Each column in the relational table defines named data fields or attributes.

  A collection of related tables in the relational model makes up a database. The mathematical theory of relations underlies the relational model - both the organization of data and the languages that manipulate the data. Edgar Codd, then at IBM, developed the relational model in 1973. It has been popular, in terms of commercial use, since the early 1980s.

• Hierarchical Model: The hierarchical data model organizes data in a tree structure. There is a hierarchy of parent and child data segments. This structure implies that a record can have repeating information, generally in the child data segments. For example, an organization might store information about an employee, such as name, employee number, department, salary. The organization might also store information about an employee's children, such as name and date of birth. The employee and children data forms a hierarchy, where the employee data represents the parent segment and the children data represents the child segment. If an employee has three children, then there would be three child segments associated with one employee segment. In a hierarchical database the parent-child relationship is one-to-many. This restricts a child segment to having only one parent segment. Hierarchical DBMSs were popular from the late 1960s, with the introduction of IBM's Information Management System (IMS) DBMS, through the 1970s.
• Network Model: The popularity of the network data model coincided with the popularity of the hierarchical data model. Some data was more naturally modeled with more than one parent per child. So, the network model permitted the modeling of many-to-many relationships in data. In 1971, the Conference on Data Systems Languages (CODASYL) formally defined the network model. The basic data modeling construct in the network model is the set construct. A set consists of an owner record type, a set name, and a member record type. A member record type can have that role in more than one set, hence the multi-parent concept is supported. An owner record type can also be a member or owner in another set. The CODASYL network model is based on mathematical set theory.
• Object-Oriented Model: An Object-Oriented Database Management System (OODBMS) must be both a DBMS and an object-oriented system. As a DBMS it must provide the capabilities identified above. OODBMSs typically can model tabular data, complex data, hierarchical data, and networks of data. The following are important features of an object-oriented system:
  • Complex objects: e.g., objects may be composed of other objects.
  • Object identity: each object has a unique identifier external to the data.
  • Encapsulation: an object consists of data and the programs (or methods) that manipulate it.
  • Types or classes: a class is a collection of similar objects.
  • Inheritance: subclasses inherit data attributes and methods from classes.
  • Overriding with late binding: the method particular to a subclass can override the method of a class at run time.
  • Extensibility: e.g., a user may define new objects.
  • Computational completeness: a general-purpose language (such as Ada, C, or C++) is computationally complete. The special-purpose language SQL is not. Most OODBMSs incorporate a general-purpose programming language.
• Flat Files: A flat file system is usually closely associated with a storage access method. An example is IBM's Indexed Sequential Access Method (ISAM). The models discussed earlier in this section are logical data models; flat files require the user to work with the physical layout of the data on a storage device. For example, the user must know the exact location of a data item in a record. In addition, flat files do not provide all of the services of a DBMS, such as naming of data, elimination of redundancy, and concurrency control. Further, there is no independence of the data and the application program. The application program must know the physical layout of the data.

Distributed DBMSs

A distributed DBMS manages a database that is spread over more than one platform. The database can be based on any of the data models discussed above (except the flat file). The database can be replicated, partitioned, or a combination of both. A replicated database is one in which full or partial copies of the database exist on the different platforms. A partitioned database is one in which part of the database is on one platform and parts are on other platforms. The partitioning of a database can be vertical or horizontal. A vertical partitioning puts some fields and the associated data on one platform and some fields and the associated data on another platform. For example, consider a database with the following fields: employee ID, employee name, department, number of dependents, project assigned, salary rate, tax rate. One vertical partitioning might place employee ID, number of dependents, salary rate, and tax rate on one platform and employee name, department, and project assigned on another platform. A horizontal partitioning might keep all the fields on all the platforms but distribute the records. For example, a database with 100,000 records might put the first 50,000 records on one platform and the second 50,000 records on a second platform.

Whether the distributed database is replicated or partitioned, a single DBMS manages the database. There is a single schema (description of the data in a database in terms of a data model; e.g., relational) for a distributed database. The distribution of the database is generally transparent to the user. The term "distributed DBMS" implies homogeneity.

Distributed Heterogeneous DBMSs

A distributed, heterogeneous database system is a set of independent databases, each with its own DBMS, presented to users as a single database and system. "Federated" is used synonymously with "distributed heterogeneous". The heterogeneity refers to differences in data models (e.g., network and relational), DBMSs from different suppliers, different hardware platforms, or other differences. The simplest kinds of federated database systems are commonly called "gateways". In a gateway, one vendor (e.g., Oracle) provides single-direction access through its DBMS to another database managed by a different vendor's DBMS (e.g., IBM's DB2). The two DBMSs need not share the same data model. For example, many RDBMS vendors provide gateways to hierarchical and network DBMSs.

There are federated database systems both on the market and in research that provide more general access to diverse DBMSs. These systems generally provide a schema integration component to integrate the schemas of the diverse databases and present them to the users as a single database, a query management component to distribute queries to the different DBMSs in the federation, and a transaction management component, to distribute and manage the changes to the various databases in the federation.

35.20.3.2 Data Dictionary/Directory Systems

The second component providing data management services, the Data Dictionary/Directory System (DD/DS), consists of utilities and systems necessary to catalog, document, manage, and use metadata (data about data). An example of metadata is the following definition: a six-character long alphanumeric string, for which the first character is a letter of the alphabet and each of the remaining five characters is an integer between 0 and 9; the name for the string is "employee ID" . The DD/DS utilities make use of special files that contain the database schema. (A schema, using metadata, defines the content and structure of a database.) This schema is represented by a set of tables resulting from the compilation of Data Definition Language (DDL) statements. The DD/DS is normally provided as part of a DBMS but is sometimes available from alternate sources. In the management of distributed data, distribution information may also be maintained in the network directory system. In this case, the interface between the DD/DS and the network directory system would be through the API of the network services component on the platform.

In current environments, data dictionaries are usually integrated with the DBMS, and directory systems are typically limited to a single platform. Network directories are used to expand the DD/DS realms. The relationship between the DD/DS and the network directory is an intricate combination of physical and logical sources of data.

35.20.3.3 Data Administration

Data administration properly addresses the Data Architecture, which is outside the scope of TOGAF. We discuss it briefly here because of areas of overlap. It is concerned with all of the data resources of an enterprise, and as such there are overlaps with data management, which addresses data in databases. Two specific areas of overlap are the repository and database administration, which are discussed briefly below.

Repository

A repository is a system that manages all of the data of an enterprise, which includes data and process models and other enterprise information. Hence, the data in a repository is much more extensive than that in a DD/DS, which generally defines only the data making up a database.

Database Administration

Data administration and database administration are complementary processes. Data administration is responsible for data, data structure, and integration of data and processes. Database administration, on the other hand, includes the physical design, development, implementation, security, and maintenance of the physical databases. Database administration is responsible for managing and enforcing the enterprise's policies related to individual databases.

35.20.3.4 Data Security

The third component providing data management services is data security. This includes procedures and technology measures implemented to prevent unauthorized access, modification, use, and dissemination of data stored or processed by a computer system. Data security also includes data integrity (i.e., preserving the accuracy and validity of the data), and protecting the system from physical harm (including preventative measures and recovery procedures).

Authorization control allows only authorized users to have access to the database at the appropriate level. Guidelines and procedures can be established for accountability, levels of control, and type of control. Authorization control for database systems differs from that in traditional file systems because, in a database system, it is not uncommon for different users to have different rights to the same data. This requirement encompasses the ability to specify subsets of data and to distinguish between groups of users. In addition, decentralized control of authorizations is of particular importance for distributed systems.

Data protection is necessary to prevent unauthorized users from understanding the content of the database. Data encryption, as one of the primary methods for protecting data, is useful for both information stored on disk and for information exchanged on a network.

35.21 Developing an Enterprise Manageability View

The Enterprise Manageability view is concerned with operations, administration, and management of the system.

35.21.1 Stakeholders and Concerns

This view should be developed for the operations, administration, and management personnel of the system.

Major concerns for these stakeholders are understanding how the system is managed as a whole, and how all components of the system are managed. The key concern is managing change in the system and predicting necessary preventative maintenance.

In general, these stakeholders are concerned with ensuring that the availability of the system does not suffer when changes occur. Managing the system includes managing components such as:

• Security components
• Data assets
• Software assets
• Hardware assets
• Networking assets

35.21.2 Developing the View

Business scenarios are an extremely useful way to depict what should happen when planned and unplanned events occur. It is highly recommended that business scenarios be created for planned change, and for unplanned change.

The following paragraphs describe some of the key issues that the architect might consider when constructing business scenarios.

35.21.3 Key Issues

The Enterprise Manageability view acts as a check and balance on the difficulties and day-to-day running costs of systems built within the new architecture. Often, system management is not considered until after all the important purchasing and development decisions have been taken, and taking a separate management view at an early stage in architecture development is one way to avoid this pitfall. It is good practice to develop the Enterprise Manageability view with close consideration of the System Engineering view since, in general, management is difficult to retrofit into an existing design.

Key elements of the Enterprise Manageability view are:

• The policies, procedures, and guidelines that drive your management requirements (such as a policy to restrict downloading software from the Internet)
• How your shop measures system availability
• The management services and utilities required
• The likely quantity, quality, and location of management and support personnel
• The ability of users to take on system management tasks, such as password maintenance
• The manageability of existing and planned components in each of the component categories
• Whether management should be centralized or distributed
• Whether security is the responsibility of system managers or a separate group, bearing in mind any legal requirements

Key technical components categories that are the subject of the Enterprise Manageability view deal with change, either planned upgrades, or unplanned outages. The following table lists specific concerns for each component category.

35.22 Developing an Acquirer View

The Acquirer view is concerned with acquiring Commercial Off-The-Shelf (COTS) software and hardware.

35.22.1 Stakeholders and Concerns

This view should be developed for personnel involved in the acquisition of any components of the subject architecture.

Major concerns for these stakeholders are understanding what building blocks of the architecture can be bought, and what constraints (or rules) exist that are relevant to the purchase. The acquirer will shop with multiple vendors looking for the best cost solution while adhering to the constraints (or rules) applied by the architecture, such as standards.

The key concern is to make purchasing decisions that fit the architecture, and thereby to reduce the risk of added costs arising from non-compliant components.

35.22.2 Developing the View

The Acquirer view is normally represented as an architecture of Solution Building Blocks (SBBs), supplemented by views of the standards to be adhered to by individual building blocks.

35.22.3 Key Issues

The acquirer typically executes a process similar to the one below. Within the step descriptions we can see the concerns and issues that the acquirer faces.

Footnotes

1. Basic Architectural Concepts is reprinted, with permission, from IEEE Std 1471-2000, Systems and Software Engineering - Recommended Practice for Architectural Description of Software-intensive Systems, Copyright© 2000, by IEEE. The IEEE disclaims any responsibility or liability resulting from the placement and use in the described manner.
2. These are different from two and three-tiered system architectures in which the middle tier is usually middleware. In the approach being presented here, middleware is seen as an enabler for the software components to interact with each other. See 35.17.2.8 Infrastructure Bus for more details.
3. If, for example, SQL statements are to be embedded in the business logic.
4. Note that typical "layered" architectures require each layer to be a client of the layer below it and a server to the layer above it. The scheme presented here is not compliant with this description and therefore we have used the word "tier" instead of "layer".
5. The interface to the data store might utilize embedded SQL. A more flexible way would be to use the Distributed Relational Database Architecture (DRDA) or ODBC since either of these standards would enable an application to access different DBMSs in a location-independent manner using the same SQL statements.
6. Although it could use other mechanisms. For example, the DAI could be built as a shared library to be linked with the application logic at compile time.
7. The security server itself would use a five-tier architecture. The security application logic tier would interface with the DAI of other systems to provide data access control.
8. For example, many people believe that the user interface should be built on COM, while the data access tiers should be built on CORBA.

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