Re: signals

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From: robert france (france@CS.ColoState.EDU)
Date: Thu 26 Sep 2002 - 15:58:16 BST

Good, that's my understanding as well. I was a bit confused about the
original email about activity diagrams and signals - Esha, can you point
to the part of the UML standard that restricts activity diagrams
to signals?


>Date: Thu, 26 Sep 2002 16:22:38 +0200
>From: Shane Sendall <>
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>Subject: Re: signals
>Hi Esha,
>I haven't as such worked on activity diagrams, but I can offer my 
>understanding of the relationship between signals and events (and 
>stimuli) in the context of statemachines.
>My understanding (of UML 1.4 spec) is that everything sent between 
>instances (of actors/objects, etc.) are stimuli. Stimuli are caused by 
>send or call actions.
>Considering just the case of Signals, a send action is executed on the 
>source instance, and consequently, a stimulus is created according to 
>the related Signal (its just the specification of the stimulus that 
>defines the signature; like a class for an object) and delivered to the 
>target instance. The Reception at the target side determines whether the 
>stimulus can be accepted (i.e., if it is supported by the classifier); 
>if it is accepted by the Reception, then a SignalEvent instance is 
>generated and placed on the state machine's event queue ready for 
>I hope that helps.
>Best of luck,
>    Shane
>- Shane Sendall - Swiss Federal Institute of Technology in Lausanne -
>- email : -
>- phone : ++41 21 693 66 89         fax : ++41 21 693 50 79         -
>Esha Ray wrote:
>> Hi!
>> I am student at UMass, Amherst and I am working with LASER(Lab for 
>> Advanced Software Engineering Research). I am working with activity 
>> diagrams and tring desperately to understand its semantics. We are 
>> really stuck with signals right now. The UML user guide, reference 
>> manual give very ambigous statemnets about signals. They also say that 
>> acticity diagrams do not have events but only signals. I am not clear 
>> on teh exact semantics about signals. Signals are also classifiers and 
>> we can have a class diagram on the hierarchy of signals int he system. 
>> Can anyone please tell me what exactly signals do in an activity 
>> diagram and how are they interpreted.
>> -Esha

Robert B. France, Assoc Professor | Tel: 970-491-6356
Computer Science Department       | Fax: 970-491-2466
Colorado State University         | Email:
Fort Collins, CO 80523            |

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