This chapter looks at the process of managing architecture requirements throughout the ADM.

Objective

To define a process whereby requirements for enterprise architecture are identified, stored, and fed into and out of the relevant ADM phases.

Approach

General

As indicated by the "Requirements Management" circle at the center of the ADM graphic, the ADM is continuously driven by the requirements management process.

It is important to note that the Requirements Management circle denotes, not a static set of requirements, but a dynamic process whereby requirements for enterprise architecture and subsequent changes to those requirements are identified, stored, and fed into and out of the relevant ADM phases.

The ability to deal with changes in requirements is crucial. Architecture is an activity that by its very nature deals with uncertainty and change - the "grey area" between what stakeholders aspire to and what can be specified and engineered as a solution. Architecture requirements are therefore invariably subject to change in practice. Moreover, architecture often deals with drivers and constraints, many of which by their very nature are beyond the control of the enterprise (changing market conditions, new legislation, etc.), and which can produce changes in requirements in an unforeseen manner.

Note also that the requirements management process itself does not dispose of, address, or prioritize any requirements: this is done within the relevant phase of the ADM. It is merely the process for managing requirements throughout the overall ADM.

Resources

The world of requirements engineering is rich with emerging recommendations and processes for requirements management. TOGAF does not mandate or recommend any specific process or tool; it simply states what an effective requirements management process should achieve (i.e., the "requirements for requirements", if you like).

Business Scenarios

One effective technique that is described in TOGAF itself is business scenarios, which are an appropriate and useful technique to discover and document business requirements, and to articulate an architectural vision that responds to those requirements. Business scenarios are described in detail in Part IV: Resource Base, Business Scenarios .

Volere Requirements Specification Template

Architecture requirements is very much a niche area within the overall requirements field. One useful resource is the Volere Requirements Specification Template, available from Volere¹ (www.volere.co.uk/template.htm). While not designed with architecture requirements in mind, this is a very useful requirements template, which is freely available and may be modified or copied (for internal use, provided the copyright is appropriately acknowledged).

One interesting item in this template is the "waiting room", which is a hold-all for requirements in waiting. There are often requirements identified which, as a result of the prioritization activity that forms part of the requirements management process (see below), are designated as beyond the planned scope, or the time available, for the current iteration of the architecture. The waiting room is a repository of future requirements. Having the ability to store such requirements helps avoid the perception that they are simply being discarded, while at the same time helping to manage expectations about what will be delivered.

Requirements Tools

There is a large, and increasing, number of Commercial Off-The-Shelf (COTS) tools available for the support of requirements management, albeit not necessarily designed for architecture requirements. The Volere web site has a very useful list of leading requirements tools (www.volere.co.uk/tools.htm).

Inputs

The inputs to the requirements management process are the requirements-related outputs from each ADM phase.

The first high-level requirements are articulated as part of the Architecture Vision, generated by means of the business scenario or analogous technique.

Each architecture domain then generates detailed design requirements specific to that domain, and potentially to other domains (for example, areas where already designed architecture domains may need to change to cater for changes in this architecture domain; constraints on other architecture domains still to be designed.)

Deliverables in later ADM phases also contain mappings to the design requirements, and may also generate new types of requirements (for example, conformance requirements, time windows for implementation).

Steps

Key steps in the requirements management process include:

Outputs

The output of the requirements management process itself is:

• A structured requirements statement, including:
  • Changed requirements
  • Requirements Impact Statement

    The requirements repository contains the current requirements for the Target Architecture. When new requirements arise, or existing ones are changed, a Requirements Impact Statement is generated, which identifies the phases of the ADM that need to be revisited to address the changes. The statement goes through various iterations until the final version, which includes the full implications of the requirements (e.g., costs, timescales, business metrics) on the architecture development.

Footnotes

1.

The Volere web site is hosted by the Atlantic Systems Guild (www.systemsguild.com).

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