Issue 8764: Section: 14.3.3 (uml2-rtf)
Source: SINTEF (Dr. Oystein Haugen, oystein.haugen(at)sintef.no)
Nature: Clarification
Severity: Significant
Summary: In sequence diagrams, the neg operator is used to describe invalid behaviours. However, people tend to interpret neg slightly differently depending on the context in which it appears, thus making it difficult to define a precise semantics for it. Two examples: A sequence diagram with a neg fragment is usually taken to describe also positive (valid) behaviours, i.e. the behaviours of the diagram with the neg fragment simply omitted. This implies that the empty trace should be positive for the neg fragment in this context. Another common use of neg is to state that one of the alternatives (operands) of an alt construct describes the invalid behaviour. In this case, the neg fragment has no positive behaviours (not even the empty trace). Recommendation: Consider introducing another operator in addition, due to the different uses of the neg operator. 

Resolution: 
Revised Text: 
Actions taken:
May 4, 2005: received issue
Discussion: 
Due to lack of time, the RTF/FTF agrees that the following are problems that need fixing, but decided to defer their resolution to a future RTF working on this specification.
End of Annotations:=====

m: webmaster@omg.org 
Date: 04 May 2005 08:56:18 -0400 
To: <issues@omg.org> 
Subject: Issue/Bug Report 



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Name: Oystein Haugen
Company: University of Oslo
mailFrom: oysteinh@ifi.uio.no
Notification: Yes
Specification: UML 2
Section: 14.3.3
FormalNumber: ptc/04-10-02
Version: 2.0
RevisionDate: 10/08/2004
Page: 508+
Nature: Clarification
Severity: Significant
HTTP User Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)
Description
In sequence diagrams, the neg operator is used to describe invalid behaviours. However, people tend to interpret neg slightly differently depending on the context in which it appears, thus making it difficult to define a precise semantics for it. Two examples: A sequence diagram with a neg fragment is usually taken to describe also positive (valid) behaviours, i.e. the behaviours of the diagram with the neg fragment simply omitted. This implies that the empty trace should be positive for the neg fragment in this context. Another common use of neg is to state that one of the alternatives (operands) of an alt construct describes the invalid behaviour. In this case, the neg fragment has no positive behaviours (not even the empty trace). Recommendation: Consider introducing another operator in addition, due to the different uses of the neg operator.