2.3 UML and Software Development Lifecycles

The typical software development process consists of several phases: requirements-gathering, high-level design, low-level design, coding and unit testing, integration testing, and deployment. Different methodologies divide these areas into different categories and subdivisions.

UML provides several diagram types that fit into each section of the Software Development Lifecycle (SDLC). Here's an overview of the diagram types we address in this chapter, in roughly the order they enter the development process:

Use case diagrams

Used through the high-level design phase to identify common sets of activities that users of the system indulge in. Use case diagrams also describe the participants in each use case. Use cases are helpful when developing test plans.

Class diagrams

Used as early as the high-level design process to define the domain model for the application: specifically, the relationship of data objects within the system, the relationships between them, and the operations that they can perform or that can be performed on them.

Interaction diagrams

Sometimes used during the requirements gathering process but particularly used in high- and low-level design to show the interactions between objects in the system. Interaction diagrams are also very helpful in the testing state when creating testing processes and procedures.

Activity diagrams

Used during requirements gathering and high-level design to further identify process flows within the system. Unlike program flow charts, activity diagrams include users and activities beyond the code itself, and allow clear delineation of the roles played by various participants.

Deployment diagrams

Used during the high-level design phase to indicate how a system will be distributed across physical resources, and during the deployment phase to document that configuration.

The rest of this chapter explores the diagram types in more detail.