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RE: isa and hasa in UML

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Fri, 30 May 2003 14:15:54 -0500
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E01817E5D@bocnte2k3.boc.chevrontexaco.net>
To: "Martin Chapman" <martin.chapman@oracle.com>, "Francis McCabe" <fgm@fla.fujitsu.com>, www-ws-arch@w3.org

How can you give up when you haven't started?  All I am asking you to do
is to go beyond saying "there exists a definition" and tell us what it
is.  If you are implying that for me to find out would be easy if I just
looked at the tools and/or books -- well, then, it should be trivial for
you since I assume you already have the tools and books (and I don't).
It sort of sounds to me like Frank is, indeed, looking at the tools
and/or books and so far he's giving me a headache.  And Walden is not
helping by saying it's really OK to equate yeti's and unicorns.  At the
risk of being swallowed by the trout, it seems to me that given a
hypothetical realization in front of me I could easily distinguish
whether it were one or the other, based on my conceptual understanding
of yeti-ness and unicorn-ness.  Or are is this about whether we believe
in Platonic forms or whatever the alternative is?  The concept versus
the realization or whatever?  If so, I think we've gone too far.  

Anyway, back to the point, so far you have not suggested any definition,
or description, of the terms, you have only objected to those which
others have proposed (and used).  I think that I am making a reasonable
request.  Propose your own definition, or description of how the term
should be understood differently than in the current document, or stop
objecting.  This is not a theoretical thing -- I honestly would like to
understand what the term means if we use it, and so far I have no idea
what you think it means.

-----Original Message-----
From: Martin Chapman [mailto:martin.chapman@oracle.com] 
Sent: Friday, May 30, 2003 1:53 PM
To: Cutler, Roger (RogerCutler); Francis McCabe; www-ws-arch@w3.org
Subject: RE: isa and hasa in UML


i give up on this.
there is a standard out there which a number of tools support, planty of
books to read. So instead we invent our own notation - crazy.

Martin.

> -----Original Message-----
> From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On
> Behalf Of Cutler, Roger (RogerCutler)
> Sent: Friday, May 30, 2003 11:40 AM
> To: Martin Chapman; Francis McCabe; www-ws-arch@w3.org
> Subject: RE: isa and hasa in UML
>
>
>
> There are concise definitions of is-a and has-a in the "old" doc.  If 
> you don't like them, it seems to me that you should come up with a 
> better alternative.  Failing that, I suggest that we continue with 
> what we have.
>
> -----Original Message-----
> From: Martin Chapman [mailto:martin.chapman@oracle.com]
> Sent: Friday, May 30, 2003 1:34 PM
> To: Cutler, Roger (RogerCutler); Francis McCabe; www-ws-arch@w3.org
> Subject: RE: isa and hasa in UML
>
>
> and how is is-a and has-a as defined in our doc any less or more 
> powerful than uml. its all about set theory and if you choose to model

> bad sets thats up to you.
>
> Martin.
>
> > -----Original Message-----
> > From: www-ws-arch-request@w3.org 
> > [mailto:www-ws-arch-request@w3.org]On
> > Behalf Of Cutler, Roger (RogerCutler)
> > Sent: Friday, May 30, 2003 10:43 AM
> > To: Francis McCabe; www-ws-arch@w3.org
> > Subject: RE: isa and hasa in UML
> >
> >
> >
> > This is REALLY discouraging.  I thought that the UML experts in the 
> > room at Rennes were saying that "everybody knows" what has-a means 
> > in UML, and all you have to do is strip it out of your favorite 
> > undergraduate textbook.
> >
> > I have a strong feeling of distaste for ditching the definition of 
> > "has-a" currently in the document, which at least has the virtue 
> > that I can understand and apply it, in favor of a definition that 
> > appears to be like the Indian rope trick -- something that everybody

> > knows exists because somebody else has seen it.
> >
> > -----Original Message-----
> > From: Francis McCabe [mailto:fgm@fla.fujitsu.com]
> > Sent: Friday, May 30, 2003 12:01 PM
> > To: www-ws-arch@w3.org
> > Subject: isa and hasa in UML
> >
> >
> >
> > This is in partial fulfillment of my action item re is-a and has-a 
> > w.r.t. UML
> >
> > 0. There is a rather (unintentionally) funny comment in the UML 2.0
> > spec:
> >
> > 2.3.2.3 Semantics
> >    The meanings of the constructs are defined using natural 
> > language. ...
> >
> > (This is after a lot of promises of being formal.)
> >
> >    However, UML uses OCL for those cases where natural language is 
> > not
>
> > enough. OCL is similar to a first order predicate calculus. Having 
> > said that, the spec does not use OCL very often; including for the 
> > definition of relationships such as generalization (is-a) and 
> > association (has-a kind of)
> >
> > 1. As I have indicated earlier, UML does not have a precise notion 
> > of is-a. The closest is the generalization relationship. This is 
> > defined in 3.50:
> >
> > Generalization is the taxonomic relationship between a more general 
> > element and a more specific element that is fully consistent and 
> > that adds additional information.
> >
> > A couple of comments:
> >
> > 1. Basing is-a on taxonomics raises some serious logical issues. 
> > This is analogous to basing everything on sets: every member of the 
> > penguin
>
> > set is also a member of the bird set.
> >
> > The problem is that it becomes really difficult to talk about weird 
> > or
>
> > abstract sets. Basing is-a on this would lead to the following 
> > counter-intuitive result: every unicorn is a yeti. (There are no 
> > documented instances of either, so the set of unicorns and yetis is
> > indistinguishable.)
> >
> > A more serious issue, sticking with birds for the moment, is that it

> > is similarly hard to talk about properties of birds such as flying: 
> > we
>
> > could not express the fact that all birds except penguins fly.
> >
> > An even more serious issue is that we need to capture the following
> > situation:
> >
> > A service has an identifier
> >
> > A Web service is a service
> > A Web service has a URI
> >
> > The Web service's URI counts_as the service identifier
> >
> > It is that counts_as that is beyond the capabilities of UML's 
> > generalization. We *could* extend UML's generalization, and that may

> > be the best overall approach. In fact, we would really need to do 
> > that
>
> > for all our relationships, use <is-a> and <has-a> and *never* rely 
> > on UML's built-in relationships. <is-a> and <has-a> could probably 
> > be defined in OCL.
> >
> >
> > More to follow....
> > Frank
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
>
Received on Friday, 30 May 2003 15:16:30 GMT

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