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UML: Use Case diagram semantics

Philip Pomario
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Joined: Oct 03, 2003
Posts: 113
Guys, I have a question haunting me since Software Modeling class in college:

What's the semantic of two Actors connected directly to the same Use Case?

A professor that I respect a lot insisted that it means that both actors are involved SIMULTANEOUSLY in the use case. I, on the other hand, read the whole UML 2.0 spec on Use Cases and that isn't stated - as far as I could find - and some places (including Cade's book) infer that either actor can use the Use Case (NOT simultaneously).

What do you think? I would appreciate a lot your comments and argumentations, as I don't think there's a definitive, absolute answer here.
[ May 02, 2007: Message edited by: Filipe Pomar ]
Frank Kuepper
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Joined: Mar 16, 2007
Posts: 45
An association exists whenever an actor is involved with an interaction described by a use case.
[ May 03, 2007: Message edited by: Frank Kuepper ]

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Philip Pomario
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Joined: Oct 03, 2003
Posts: 113
Originally posted by Frank Kuepper:
An association exists whenever an actor is involved with an interaction described by a use case.


Yup, that's for sure. But whenever I graphically see two actors associated with a Use Case, do I know for sure (without looking at the textual description) that BOTH actors are involved at the SAME TIME in realizing the Use Case? Or can I infer that the two actors can use the Use Case independently?
[ May 03, 2007: Message edited by: Filipe Pomar ]
Jan Cumps
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Joined: Dec 20, 2006
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    7

But whenever I graphically see two actors associated with a Use Case, do I know for sure (without looking at the textual description) that BOTH actors are involved at the SAME TIME in realizing the Use Case? Or can I infer that the two actors can use the Use Case independently?
It can mean both.

They might both be required to complete the use case.
They might both be able to use the use case.

Craig Larman (in Applying UML and Patterns, Third edition, p.91) advises to draw primary actors left of the use case, and supporting actors on the right.

Regards, Jan


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Philip Pomario
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Joined: Oct 03, 2003
Posts: 113

Craig Larman (in Applying UML and Patterns, Third edition, p.91) advises to draw primary actors left of the use case, and supporting actors on the right.


Jan, Craig doesn't state that, at least on my edition of the book. In fact, all he explicitly writes regarding this topic is the following (which still doesn't help):

A common sign of a novice (or academic) use case modeler is a preoccupation with use case diagrams and use case relationships, rather than writing text. World-class use case experts such as Fowler and Cockburn, among others, downplay use case diagrams and use case relationships, and instead focus on writing.

I'm still very curious about what you all think. Your thoughts are much appreciated.


Regards,
Filipe
Jan Cumps
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    7

Craig doesn't state that, at least on my edition of the book.
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