System Sequence Diagrams (SSD) Overview

Steps for Developing SSDs

• Identify input message: Analyze the use case flow (or activity diagram) to determine the message the external actor sends to the system.
• Describe the message: Use a verb-noun format to name the message representing the action the system is performing. Include any necessary parameters.
• Special conditions: Identify any specific conditions, such as loops (iteration/loop frame) or alternative scenarios (opt/alt frame).
• Output return values: Determine if the system returns a value and whether this returns as an explicit value on a separate line or within the message itself.

System Sequence Diagram (SSD)

• Illustrates input and output events: SSDs show events (from external actors) in a particular use case scenario. The order and inter-system events are illustrated.
• Black-box perspective: The system is viewed as a black box, with emphasis on external interactions. SSDs show the interactions and not the internal workings of the system.
• Derived from use cases: They are often drawn for major scenarios in a use case and frequent/complex alternative ones.
• Input for object design: SSDs provide information that can be used to design objects and their interactions within the system.

System Events and System Operations

• System operations: High-level actions a system provides to the outside world. External actors trigger system operations via input events.
• Assignment to conceptual class: In system behavior analysis, these operations are associated with system classes for understanding.
• Parameter handling: When a message doesn't require parameters from the sender, this is handled with no brackets during communication. This is not a universal standard.

This quiz focuses on the development and understanding of System Sequence Diagrams (SSD). Participants will explore the steps for identifying input messages, describing actions, handling special conditions, and determining output return values. It provides a clear understanding of how SSDs illustrate system interactions from an external actor's perspective.