RE: [discussion@2uworks.org] RE: [wg@2uworks.org] 3C + 2U = xP?



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From: Tony Simons (A.Simons@dcs.shef.ac.uk)
Date: Sat 07 Sep 2002 - 18:17:16 BST


Hi again,

Joaquin Miller wrote:

=====
> > >A consequence of the semantic domain design principles is that the
> > >semantic domain should not contain equivalences; i.e. all semantic
> > >elements denote distinct concepts.

One possible reading:
   semantic elements are the items in the semantic domain
   the items in the semantic domain denote concepts
=====

Well I can't really comment on the wording of the 2U document, but I
I read this as meaning that each element in the semantic domain is
unique (not equivalent to any other in the domain) and therefore a
denotation of a distinct element from the UML model.  I don't think 
that there's meant to be another level of concepts below the semantic 
domain, which somehow explains that domain.  Granted, the wording does 
seem a bit fluffy.

It would have been easier to say:  "Because of the way the semantic
domain is constructed, elements in the domain are unique.  No element
is equivalent to any other."

This would have avoided introducing "concepts" which seems to be the
source of the confusion.  I haven't seen the full context of the above
statement, but the "concepts" may refer to UML model elements, in which
case I would read this as meaning: "if two model elements are denoted
by different semantic elements, then they are distinct".

My preferred answers to your questions are therefore:

>  Which are the concepts that the items in the semantic domain (the 
> "semantic elements") denote?

-- elements from the semantic domain are the denotations (interpretation) 
   of UML model elements;  it is reasonable to say that they "denote the
   concepts" (from the model layer above)

>  Where are those concepts found?

-- these "concepts" are just ordinary elements of UML models, whose 
   meaning is given by the mapping to elements in the semantic domain

>  What do those concepts denote?

-- probably not a well-formed question; they model some aspect of the
   software system under consideration, but "denoting" may be the
   wrong term, since the relationship is one of abstraction rather 
   than precise characterisation.
   
>  Where do we find the meaning of those concepts?

-- well, the meaning of the concepts-as-UML-elements is given in the
   semantic domain;  the meaning of the real world/system is more
   tricky!
   
I hope this helps,

--Tony

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Dr Anthony J H Simons                   a.simons@dcs.shef.ac.uk
Senior Lecturer in Computer Science     http://www.dcs.shef.ac.uk/~ajhs
Director of Teaching

Department of Computer Science          tel:  (+44) 114 22 21838
University of Sheffield                 dept: (+44) 114 22 21800
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