activator association in a Sequence Diagram



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From: Bernardi Simona (bernardi@di.unito.it)
Date: Wed 04 Sep 2002 - 14:56:30 BST


Hello,

can anybody tell me what is  the meaning of "activator" association in the
context of sequence diagrams (if there is one) ?

The information given in the UML manual (version 1.4) seem to me
contradictory, in particular the following statements:

1- each message belonging to an interaction has got an activator message,
except for the initial messages (page 2-134)

2- the well-formed rule for Message class:
"predecessors must have the same activator as the message"
self.allPredecessors->forAll (p|p.activator = self.activator)

where self.allPredecessors is the set of all Messages that precede the
current one (i.e., self).

Since  an initial message belongs to (at
least)  a set of type "m.allPredecessors" where m is a not-initial message
belonging to the same interaction, the well-formed rule says that
the initial message has an activator.
   
Thanks,
Simona.

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