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R.UM.

Sequence Models

How we can build UML2 sequence models that can be later displayed as sequence diagrams.

Context

Often in the UML documentation [1] behavioral models are presented as part of classes.
We prefer not to link such models too strictly to a single class since we see them as representing scenarios involving instances of several classes.
Therefore we put the behavioral models in packages, or at the model root.

Model structure

After several hours spent in decrypting the standard [1], we found very useful a simple example in the Eclipse UML2 mailing list [2].
All the elements part of a sequnce model are contained within a Collaboration object; it containts:
The Interaction object provides a detailed description of the messages exchanged between the instances that are represented by placeholders: the Lifeline objects.

Overal structure of a sequence model

I still wonder what is the purpose of the Connector object and the two attached End objects, since they are not referenced anywhere in the model.

Within the Interaction messages can be modeled between Lifelines.
A message is sent through a send event (an EventOccurrence object) by a Lifeline object and it is received through a receive event (an EventOccurrence object) by a Lifeline object.
The message can have a signature (in addition to a name) that refers to an Operation object, with should be defined within the class that is the type of the instance (the Property object) represented by the receiving Lifeline object.
Structure of Interaction sequence model

References

[1]
 OMG - UML2 Superstructure Specification - V2.0, October 8, 2004
available at: http://www.omg.org/cgi-bin/doc?ptc/2004-10-02.
[2]
 Eclipse UML2 Newsgroup - Message #1168, February 8, 2005
available at: http://www.eclipse.org/newsportal/article.php?id=1168&group=eclipse.tools.uml2#1168.


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