Is there a way to show an if statement in a UML Sequence Diagram?

Question

I went on an interview last year and was shown a sequence diagram and was asked to describe the the sequence. There were 2 things in the diagram I had never seen before. I asked what one of them was and was told that's how an if statement is shown in a sequence diagram. The other was an arrow going back to the actor that originated the arrow, I assumed that was a loop.

1. Is there a standard way to show a conditional sequence?
2. How often is a conditional sequence used in UML sequence diagrams?

• Nikki9696: UML 2.0? ibm.com/developerworks/rational/library/3101.html
• user53141: If you start wanting to put conditions in sequence diagrams, your sequence diagrams are probably two complex. Generally, you create a diagram for the "Happy Path" and maybe a couple for common error cases.

Answer 1

1.Is there a standard way to show a conditional sequence?

Yes. You can use the If else condition, also called alternatives in UML terms.

2.How often is a conditional sequence used in UML sequence diagrams? Every time there is the need to explain the choice between two or more message sequences.

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