How to show possible actions in an activity diagram?

Question

I am trying to depict an application in an activity diagram. It is about membership to an association. Both the member and association can cancel the membership of that member. I am not sure how to depict it.

There are three action flow beginning make member activity, finish as member, cancel membership by member and cancel membership by assoc. Is it a true representation? Three of the action flow are possible and only one can come true. I thought using black boxes but it is said to depict parallel activities. Or instead should I use decision diomand? What is the best depistion for this scenerio?

Answer 1

If you want to show the business flow using activity diagram, you're missing the crucial part of participating as a member. With the current diagram you immediately jump from becoming a member to cancelling the membership, and that's probably not what you wanted to depict. In addition, two arrows coming out of an action is an implicit fork, so both member and association would have to perform the cancellation in parallel to finish the flow.

Based on your question I am assuming that you wanted to show what actions are possible in general in the system. In such case your preferred diagram should be the use case diagram rather than an activity diagram.

If you insist on using activity diagram, add an intermediary action (something like "perform membership duties" or whatever it is), followed by a decision node (a diamond), that will then have outgoing edges to both cancellation options. Make sure to add conditions on those edges.