Design Principles

Key design principles

The proposal maximizes the commonality of services (for example, creation of objects, invocation of operations, event reporting and distribution) used for interworking scenarios and for pure CORBA environment scenarios.

Also, some specific guiding principles have been consistently applied when trying to resolve the issues encountered:

• Completeness
  The aim is to provide as complete a set of services as possible, covering all possible cases and specific functionality, regardless of the frequency.

• Simplicity
  There are certain scenarios and services that are more common than others. Given the completeness principle, all cases should be covered. However, the most common cases should be covered with the simplest approach, at the expense of potentially complicating the less common situations. This is also known as the 80-20 rule.

• Reuse of OMG specifications and services
  Rather than inventing new approaches to do the same thing, already existing OMG specifications have been reused whenever possible.

• Freedom of implementation
  This document does not impose any particular implementation policy, and does not constrain implementations in any way unless it is absolutely necessary. Although the discussions to arrive to any specific design solution always take into account the feasibility of implementations, the document tries not to provide any implementation bias.

Alignment with CORBA Design Principles

• Uses and builds on CORBA concepts:

  • Separation of interface and implementation

  • Object references are typed by interfaces

  • Clients depend on interfaces, not implementations

  • Use of multiple inheritance of interfaces

  • Use of subtyping to extend, evolve and specialize functionality

  • Finding a service is orthogonal to using it

  • Factories, factory finders and use of federation of services or traders

• Assumes good ORB and Object Services implementations:
  Specifically, it is assumed that CORBA-compliant ORB implementations are being built that support efficient local and remote access to both fine-grain and coarse-grain objects, and have performance characteristics that place no major barriers to the pervasive use of distributed objects for virtually all service and application elements.

• Allows Local and Remote Implementations:
  In general the services are structured as CORBA objects with OMG IDL interfaces that can be accessed locally or remotely and which can have local library or remote server styles of implementations. This allows considerable flexibility as regards the location of participating objects.

• Enforces interface style consistency:

  • Use of exceptions and return codes

  • Use of explicit operations

  • Use of interface inheritance

Alignment with OSI and Internet Management

Management of a communications environment is an information processing application. Because the environment being managed is distributed, the individual components of the management activities are themselves distributed.

Management applications perform the management activities in a distributed manner, by establishing associations between systems management application entities.

The interactions which take place between systems management application entities are abstracted in terms of management operations and notifications issued by one entity to the other. These are communicated using systems management services and protocols.

Management activities are effected through the manipulation of managed objects. For the purposes of systems management, management applications are categorized as MIS-Users. Each interaction takes place between two MIS-Users, one taking the manager role, the other the agent role.

A MIS-User taking the role of an agent is that part of a distributed application that manages the managed objects within its local system environment. An agent performs management operations on managed objects as a consequence of management operations communicated from a manager. An agent may also forward notifications emitted by managed objects to a manager.

A MIS-User taking the role of a manager is that part of a distributed application which has responsibility for one or more management activities, by issuing management operations and receiving notifications.