5.5: Sequence Diagrams
The second key OO modeling diagram discussed for application in the requirements phase of the SDLC is the sequence diagram. Both use cases and sequence diagrams are behavioral types of diagrams.
During the requirements analysis phase, the system can be treated as a single "black box", meaning we can look at the system's behavior (what it does) without explaining how it does it. Watch this example of a system sequence diagram for a student admission use case.
System behavior can be described using sequence diagrams. These can help visualize the workflow and how components work with each other. Be sure to understand the main components of a sequence diagram (participants, lifelines, boxes, dividers, and interactions) and how to design it. As you read, remember that the sequence diagram is about "how", not "what". This section includes an example of a sequence diagram and presents sequence diagrams in the context of dynamic diagrams.
Software requirements tools support requirements activities: modeling, analyzing, prioritizing, classifying, managing (planning, scheduling, reviewing, and monitoring), measuring, allocating to design and implementation components, tracing, version and configuration identification and control, and validating. The modeling and diagramming tools, management, measurement, allocation, and configuration management tools are common in each SDLC phase. Formal tools provide support for analysis of correctness, completeness, and consistency; for generation of test cases, use cases, and other UML models; and for translating formal specifications diagrams to requirements specification documents.