(This is contrary to a popular misconception about this, what your use case suggests always happens in the main scenario and sometimes happens in alternate flows simply depends on what you choose as your main scenario use cases can easily be restructured to represent a different flow as the main scenario and this should not matter).
includeĪ base use case is dependent on the included use case(s) without it/them the base use case is incomplete as the included use case(s) represent sub-sequences of the interaction that may happen always OR sometimes. I’ll use the terms ‘base’, ‘included’ and ‘extending’ to refer to the use case roles. The key to Include and extend use case relationships is to realize that, common with the rest of UML, the dotted arrow between use cases is a dependency relationship. Here’s a correct approach (in my view, and checked against Jacobson, Fowler, Larmen and 10 other references). This may be contentious but the “includes are always and extends are sometimes” is a very common misconception which has almost taken over now as the de-facto meaning.
