statecharts and activity diagrams

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From: Esha Ray (
Date: Fri 27 Sep 2002 - 19:40:07 BST


We have been hearing stuff about the ambiguious semantics of the activity diagrams. Statecharts semantics are more clearly defined than activity diagrams. UML manuals say that activity diagrams are a specialised form of state diagrams. We were having a number of questions regarding this.

1. How are activity diagrams and statecharts different?

2. Is there anything in statecharts that cannot be represented by activity diagrams and is there anything in activity diagrams that statecharts can't represent (since activity diagams are specialised forms of statecharts we supposed they might be representing something more)?

3. Where will one use a statechart and not use an activity diagram and vice versa?

4. Can a system be represented by statecharts sufficiently well that we don't need activity diagrams to describe it and vice versa?

I tried looking through all UML books(refernce guide, user manual, UML Distilled, Using UML) and on the web about any precise differences between the two diagrams but did not find anything substantial. Please help if you know this.

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