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New Post 4/21/2008 7:55 AM
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User is offline vinny
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Activity Diagram: Decision or Parallel Activities? 
Modified By Adrian M.  on 4/21/2008 4:46:01 PM)

msdn2.microsoft.com/en-us/library/Aa289858.vxfm7_topleveldiagram(en-us,VS.71).gif

In the above link, the diagram goes from "Login" to making a decision which of five options to choose.  Since any of those actions could be performed while logged in, shouldn't the 'decision' node be a horizontal bar representing the start of parallel activities?

TIA,

vinny

 
New Post 4/21/2008 3:49 PM
User is offline Adrian M.
741 posts
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Re: Activity Diagram: Decision or Parallel Activities? 

 vinny wrote

msdn2.microsoft.com/en-us/library/Aa289858.vxfm7_topleveldiagram(en-us,VS.71).gif

In the above link, the diagram goes from "Login" to making a decision which of five options to choose.  Since any of those actions could be performed while logged in, shouldn't the 'decision' node be a horizontal bar representing the start of parallel activities?

TIA,

vinny

Hi Vinny,

While all those tasks can be performed only after login there is not implication whatsoever that they can be performed in parallel.  As a matter of fact, given the {OR} constraint only one of those tasks can be performed at a time.  I think the diagram is fine.

- Adrian


Adrian Marchis
Business Analyst Community Blog - Post your thoughts!
 
New Post 4/22/2008 6:45 AM
User is offline vinny
66 posts
8th Level Poster


Re: Activity Diagram: Decision or Parallel Activities? 

As always, thanks for taking the time to respond, Adrian.

I questioned the linked diagram because of what you told me in the "Parallel Activities" thread:

(3) There is no dependency between the two parallel flows.  For example: the student can "Attend the University Overview Presentation" before or after "Enrolling in Seminar(s)".

This is an "OR" scenario, isn't it?  Do I basically have a choice to either use the fork or the decision node, so long as I qualify the transitions stemming from the decision node with "{OR}"?  Or is there a difference?

Thanks for helping! 

vinny

 
New Post 4/22/2008 3:29 PM
User is offline Adrian M.
741 posts
3rd Level Poster




Re: Activity Diagram: Decision or Parallel Activities? 

Hi Vinny,

When you have the situation of multiple activities that can be performed in no particular order after a given step there are multiple ways of modeling this depending on your need.  However, in all cases you will have some type of split mechanism which controls the flow.

Generally, if only one of the following activities can be performed at a given point in time (as is in your example) I like to use a decision in the Activity Diagram (XOR gateway in BPMN).  However, if more than one following activities can be performed at the same time (regardless of order) then you'll need to use the fork in the Activity Diagram.

BPMN (and other more robust workflow notations) on the other had uses gateways for all these uses but it has more granular types of gateways.  For example:

  • XOR (exclusive OR) -> only one path can be taken after the split
  • OR (inclusive OR) -> multiple paths can be taken after the split (note that at least one path must be taken)
  • AND -> all paths are taken after the split (think of parallel paths)
  • Complex -> specific logic in the gateway specify which of the paths to take

In addition, BPMN has precise rules for how the flow continues when all those paths merge again.  BPMN has a nice way of looking at all these by considering a token which travels down the execution path.  For example, when the toke reaches an XOR gateway it goes down only one path whereas when the token reaches an AND gateway it splits into multiple tokens with each path getting one token.  When the paths join using an AND gateway the flow does not continue until all the individual token arrive at the merge at which time they become one token again and the execution continues with the next step.

Hope this helps!

- Adrian


Adrian Marchis
Business Analyst Community Blog - Post your thoughts!
 
New Post 4/23/2008 6:53 AM
User is offline vinny
66 posts
8th Level Poster


Re: Activity Diagram: Decision or Parallel Activities? 

That's precisely the clarification that I was looking for regarding Activity diagram notation usage.  And I really appreciate how you explained things in terms of BPMN as well; after I get a solid grasp on Activity diagrams, BPMN is definitely the route I'll be headed for business process modeling.

Thanks so much again, Adrian!  I can't seem to get this type of information from the books!

 
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