What is a sequence diagram and when to use it?

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Accepted Answer

**Sequence Diagram** — UML diagram showing object interactions over time. **When to use:** - To model a specific scenario or flow. - To show message ordering. - To identify objects involved in a process. - To verify use case logic. **Components:** ``` Actors/Objects: shown as lifelines Messages: arrows between lifelines - Synchronous: solid arrow (→) - Asynchronous: open arrow (->) - Return: dashed arrow (--→) Activation bars: when object is active Fragments: loop, alt, opt, par ``` **Example:** ``` User :Browser :Server :Database |---login()---->| | | | |--validate()>| | | |<--result---| | |<--token-------| | | ``` **Best for:** Detailed interaction flows, API design.

Systems Analyst: What is a sequence diagram and when to use it?