Chapter 6: System Design: Decomposing the System
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Abstract
System design is the transformation of an analysis model into a system design model. During system design, developers define the design goals of the project and decompose the system into smaller subsystems that can be realized by individual teams. Developers also select strategies for building the system, such as the hardware/software strategy, the persistent data management strategy, the global control flow, the access control policy, and the handling of boundary conditions. The result of system design is a model that includes a subsystem decomposition and a clear description of each of these strategies.
System design is not algorithmic. Developers have to make trade-offs among many design goals that often conflict with each other. They also cannot anticipate all design issues that they will face because they do not yet have a clear picture of the solution domain. System design is decomposed into several activities, each addressing part of the overall problem of decomposing the system:
- Identify design goals. Developers identify and prioritize the qualities of the system that they should optimize.
- Design the initial subsystem decomposition. Developers decompose the system into smaller parts based on the use case and analysis models. Developers use standard architectural styles as a starting point during this activity.
- Refine the subsystem decomposition to address the design goals. The initial decomposition usually does not satisfy all design goals. Developers refine it until all goals are satisfied.
In this chapter, we focus on the first two activities. In the next chapter, we refine the system decomposition and provide an in-depth example with the ARENA case study.