links & messages



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Gonzalo Genova (ggenova@ie.inf.uc3m.es)
Wed, 19 Jan 2000 15:43:47 +0100


According to UML User Guide, p. 209: "wherever there is a link between two objects, one object can send a message to the other object", and p. 210: "A link specifies a path along which one object can dispatch a message to another (or the same)". Does this mean that an object can send messages only to those objects with which it is linked? Or should we understand the word "link" less rigorously, in the sense of "association"? Were this the case, then an object OB1 of class CL1 could send a message to any object OB2 of class CL2 whenever an association AS12 exists between classes CL1 and CL2, regardless of the existence of a concrete link (association instance) between OB1 and OB2. What is the precise semantics of UML in this case? This problem is related to the question I posed some days ago (modeling link creation), in the sense that if you allow the sending of messages only through concrete links, then the question arises, How is the communication achieved between objects that are not yet linked?


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