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Topic Title: Data Flow on Activity Diagrams?
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Created On: 1-Oct-2008 20:52
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 1-Oct-2008 20:52
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Raymond Jorgensen

Posts: 4
Joined: 19-Apr-2007

Is it possible to create an activity diagram with data flow objects? The diagram has the control/sequence/transition flow capability, but I don't see any provision to add a line that represents data or signal flow.

For example, I have one activity that depends on the computational result of another activity - how do I capture this transaction of information between the activities? In early analysis, this might be just a data flow - which later will be translated into software objects. (As far as I'm concerned, a line can also represent an object, too - just from a different point of view.)

I asked Sandy Friedenthal, SysML guru from Lockheed-Martin, and he assured me that SysML does allow this, but maybe the individual tools are preventing this behavior.
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 7-Oct-2008 10:43
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Charlie Lane

Posts: 86
Joined: 16-Sep-2005

We wanted to do this too. The problem with activities in activity diagrams is that they aren't related in the model to the operations that are done in the activities, except by name.

What we ended up with was modelling the data flow separately by "Data Dependency" connections between the operations --- we make a data dependency from an operation that consumes some data to the operation that provides it. This is extended to include attributes, so we can model what operation the attribute depends on to provide its value and what operation uses the value of the attribute. Events likewise.

We set up the types/directions of the arguments of the operations and the types of the attributes using types defined in a TypesPkg. It's then a relatively simple macro to run through the model and automatically check that no data flows are left hanging.

We couldn't see how to include this on activity diagrams, but on reflection most of our activity diagrams are busy enough that we wouldn't want any more on them. If Rhapsody supported layers on diagrams that could be a different matter.
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