Activity: Design Components

This activity refines the design of the system.

Description	Work Breakdown Structure	Team Allocation	Work Product Usage

Relationships

Parent Activities	Analysis & Design

Description

This activity has the following goals:

Refine the definitions of design elements by working out the 'details' of how the design elements realize the behavior required of them.
Refine and update the use-case realizations based on new design element identified (i.e. keeping the use-case realizations updated)
Review the design

Properties

Event-Driven
Multiple Occurrences
Ongoing
Optional
Planned
Repeatable

Staffing

Typically, one person or a small team is responsible for a set of design elements, usually one or more packages or subsystems containing other design elements. This person/team is responsible for fleshing out the design details for the elements contained in the package or subsystem: completing all operation definitions and the definition of relationships to other design elements. The Task: Capsule Design focuses on the recursive decomposition of functionality in the system in terms of capsules and (passive or data) classes. The Task: Class Design focuses on refining the design of passive class design elements, while the Task: Subsystem Design focuses on the allocation of behavior mapped to the subsystem itself to contained design elements (either contained capsules and classes or subsystems). Typically subsystems are used primarily as large-grained model organization structures, while capsules being used for the bulk of the work and "ordinary" classes being relegated largely to passive stores of information.

The individuals or teams responsible for designing capsules should be knowledgeable in the implementation language as well as possessing expertise in the concurrency issues in general. Individuals responsible for designing passive classes should also be knowledgeable in the implementation language as well as in algorithms or technologies to be employed by the class. Individuals or teams responsible for subsystems should be more generalists, able to make decisions on the proper partitioning of functionality between design elements, and able to understand the inherent trade-offs involved in various design alternatives.

While the individual design elements are refined, the use-case realizations must be refined to reflect the evolving responsibilities of the design elements. Typically, one person or a small team is responsible for refining one or more related use-case realizations. As design elements are added or refined, the use-case realizations need to be reconsidered and evolved as they become outdated, or as improvements in the design model allow for simplifications in the use-case realizations. The individuals or teams responsible for use-case realizations need to have broader understanding of the behavior required by the use cases and of the trade-offs of different approaches to allocating this behavior amongst design elements. In addition, since they are responsible for selecting the elements that will perform the use cases, they need to have a deep understanding of external (public) behaviors of the design elements themselves.

Usage

Usage Guidance

Typically the work here is carried out individually or in small teams, with informal inter-group interactions where needed to communicate changes between the teams. As design elements are refined, responsibilities often shift between them, requiring simultaneous changes to a number of design elements and use-case realizations. Because of the interplay of responsibilities, it is almost impossible for design team members to work in complete isolation. To keep the design effort focused on the required behavior of the system (as expressed in use-case realizations), a typical pattern of interaction emerges:

design elements are refined by the responsible persons or teams
a small group (perhaps 2-5 people) gathers informally to work out the impact of the new design elements on a set of existing use-case realizations
changes to both the use-case realization and the participating design elements are identified
the cycle repeats until all required behavior for the iteration is designed.

Because the process itself is iterative, the criteria for 'all required behavior for the iteration' will depend on the position in the lifecycle.

Focus on architecturally-significant behaviors in the elaboration phase. Ignore all other 'details'.
In the construction phase there is a shift to completeness and consistency of the design, so that by the end of the construction phase there are no unresolved design issues.

Note that the design for an iteration does not need to be complete before beginning implementation and test activities. Partially implementing and testing a design as it evolves can be an effective means of validating and refining design, even within an iteration.