Architectural Design - Refining the Architecture into Components and Describing Instantiations of the System

Refining the Architecture into Components

As the software architecture is refined into components, structure of the system begins to emerge. Components of the software architecture are derived from three sources:
- the application domain
- the infrastructure domain
- the interface domain
Because analysis modeling does not address infrastructure, one should allocate sufficient design time to consider it carefully.
In order to find the components that are most suitable for refining the software architecture, you need to start by using the classes which were described in the analysis model. The analysis classes in turn are representations of business entities that architecture is trying to describe. You could also base these components on an infrastructure model rather than the business model. If you went purely by the business model, you would not be able to depict many of those infrastructure components such as database components, components used for communication etc.
Whatever interfaces are described in the architecture context diagram imply one or more specialized components that process the data that flow across the interface.

Describing Instantiations of the System

The context of the system has been represented, the archetypes indicating important abstractions are defined, the overall structure of system apparent and major software components are identified, however further refinement is necessary which is accomplished by developing an actual instantiation of architecture. The architecture is applied to a specific problem with the intent of demonstrating that the structure and components are appropriate.

Architectural Design - Representing the System in Context and Defining Archetypes

As architectural design begins, the design should define the external entities that the software interacts with and nature of the interaction. Once the context is modeled and all external interfaces are described, the structure of the system is specified by the designer. It is done by defining and refining software components that implement the architecture.

REPRESENTING THE SYSTEM IN CONTEXT

Architectural context represents how the software interacts with entities external to its boundaries. A system context diagram accomplishes this requirement by representing the flow of information into and out of the system. At the architectural design level, a software architect uses an architectural context diagram to model the manner in which software interacts with entities external to its boundaries.

How do systems inter-operate with the target system?
Superordinate Systems
These systems use the target system as part of some higher level processing scheme.
Subordinate Systems
These systems are used by the target system and provide data or processing that are necessary to complete target system.
Peer-level Systems
These systems interact on a peer-to-peer basis.
Actors
These entities interact with the target system by producing or consuming information necessary for requisite processing.
Each of these external entities communicates with target systems through an interface.

DEFINING ARCHETYPES

Archetypes are the abstract building blocks of an architectural design. It is a class or pattern that represents a core abstraction that is critical to design of an architecture for the target system. Archetypes can be derived by examining analysis classes defined as part of analysis model.Target system architecture is composed of these archetypes which represent stable elements of the architecture. Some kind of archetypes are:
- Nodes
- Detector
- Indicator
- Controller