Describing an If-else structure in a UML system sequence diagram

Question

Is it possible to describe an if-else structure in a system sequence diagram? If yes, how is this done?

Answer 1

Yes, this can be done in UML 2 using the 'Alternative' combined fragment type, although personally I find them relatively difficult to read. There is a good example in this IBM DeveloperWorks article.

Answer 2

Here's more info about combined fragments from the VS 2010 sequence diagram documentation:

• UML Sequence Diagrams: Reference
• UML Sequence Diagrams: Guidelines
• Describing Control Flow with Fragments in UML Sequence Diagrams