Issue 18185: UML association semantics vis-a-vis Interfaces (and other types of classifiers) (uml25-ftf)
Source: Simula Research Laboratory (Mr. Bran Selic, selic(at)acm.org)
Nature: Uncategorized Issue
Severity: 
Summary: The semantics of associations are specified in terms of links, which the UML 2.4 spec defines as: "a tuple with one value for each end of the association, where each value is an instance of the type of the end" and the 2.5 spec as "a tuple with one value for each memberEnd of the Association, where each value is an instance of the type of the end". However, the specs include several examples of associations between interfaces. Since interfaces are abstract classifiers they cannot have instances ("Interfaces may not be instantiated"), the semantics of associations whose ends terminate on interfaces cannot be described by the above semantics. 

Some other semantics need to be provided for such cases.

Furthermore, the issue extends to other types of classifiers (e.g., collaborations) where the meaning of "instance" is not straightforward.


Resolution: 
Revised Text: 
Actions taken:
October 19, 2012: received issue
Discussion: 

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Sender: bran.selic@gmail.com
From: Bran Selic <selic@acm.org>
Date: Fri, 19 Oct 2012 14:29:29 -0400
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Subject: UML association semantics vis-a-vis Interfaces (and other types of classifiers)
To: issues@omg.org
Cc: Juergen Boldt <juergen@omg.org>


The semantics of associations are specified in terms of links, which the UML 2.4 spec defines as: "a tuple with one value for each end of the association, where each value is an instance of the type of the end" and the 2.5 spec as "a tuple with one value for each memberEnd of the Association, where each value is an instance of the type of the end". However, the specs include several examples of associations between interfaces. Since interfaces are abstract classifiers they cannot have instances ("Interfaces may not be instantiated"), the semantics of associations whose ends terminate on interfaces cannot be described by the above semantics. 

Some other semantics need to be provided for such cases.

Furthermore, the issue extends to other types of classifiers (e.g., collaborations) where the meaning of "instance" is not straightforward.