CODEWITHSUNDEEP
algorithmumlmodeling
Mr. Boy
Mr. Boy

Reputation: 63806

How to use an activity diagram to detail classes & methods?

I wish to document code for a fairly complex algorithm whose implementation is intertwined across several methods and classes. A sequence diagram cannot really describe the detail of each method well so I am looking at an activity diagram; however this doesn't typically seem to represent classes and methods, only the logic.

Is there a common or even proper way to show which methods the logic belongs to? I do not need to follow strict UML, the purpose is simply to make it clear what's happening visually.

Upvotes: 2

Views: 669

Answers (1)

Christophe
Christophe

Reputation: 73510

Activity diagrams and partitions

The activity diagram are supposed to models activities without necessarily relating them to classes/objects. They are however very suitable for modeling complex algorithms, as they allows to show :

  • the control flow -- flowchart diagrams have proven effective for modeling alorthims; activity diagrams are much more precise in their semantic and can do this as well.
  • object flows that show what objects are passed through
  • there are object actions that are specifically meant for dealing with objects

Activity diagrams support partitions, i.e. visual grouping of activities according to a criteria. A popular use is to split actions by using subsystems as grouping criteria. Breaking down by classes seems overkill, but nothing forbids such groupings if it helps, and if you're able to use it consistently.

Interaction overview diagrams

Interaction Overview Diagrams are specialization of Activity Diagrams that represent Interactions.

Interaction overview diagrams are a kind of combination of activity and sequence diagrams. The general idea is to use some activity modeling features for showing the big picture of the flows, between interaction nodes, i.e. mini sequence diagrams embedded in the larger diagram, to show which objects are involved and what messages they exchange.

There is an inspiring example here. But be careful: the linked website is based on a former version of UML and the text is not fully up-to-date. The most accurate source on these diagrams is section 17.10 of the UML 2.5.1 specs.

Additional thoughts

Instead of trying to show everything in one diagram, you may prefer the beauty of simplicity: use an easy to understand, simpler overview diagram, and uncover the complexity in additional diagrams that focus on details. This works with activity diagram complements with more detailed activities or sequence diagrams. But it also works the other way round, showing exchanges between key objects in a sequence diagram, and provide more detailed activity diagrams to describe what happens inside of one of the invoked operation.

Disclaimer: While I provide some hints that you can use to model algorithms in relation with their classes, I have at the same time to warn you that visual programming, i.e. a very very very detailed modeling, may lead to very complex diagrams that are difficult to read, and even more difficult to maintain. They loose the benefit of communicating the big picture. I'm not alone in this criticism, see Grady Booch who knows what he is talking about, since he is one of the co-inventor of UML, Martin Fowler, and many others

Upvotes: 1

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