I had to show a confirmation message in one of my activity diagrams recently, and I was a little confused as to the best way to do this. I’m sure a lot of you have encountered this where you have an action followed by a simultaneous confirmation message, and an initiation of another action.
The best way to show this is to have a fork, and then start off the two things in parallel, but since showing the confirmation message is pretty much the end of the first action, I wasn’t sure if it is allowed to use a fork because there would be no join in this case.
The good news however is that you are indeed allowed to use a fork without a join without flouting any UML 2.5 standards. It is recommended that you have a join when you have a fork but in cases where it doesn’t make sense to do so – you are okay in using a fork without a join.
Relevant excerpt from perhaps the most useful website on activity diagram modeling:
A Fork Should Have a Corresponding Join. In general, for every start (fork) there is an end (join). In UML 2 it is not required to have a join, but it usually makes sense.
In my opinion this is the best way to show confirmation messages in this type of diagram, but if you know of a better one, please do leave a comment!