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RE: isa and hasa in UML

From: Martin Chapman <martin.chapman@oracle.com>
Date: Fri, 30 May 2003 11:53:07 -0700
To: "Cutler, Roger \(RogerCutler\)" <RogerCutler@chevrontexaco.com>, "Francis McCabe" <fgm@fla.fujitsu.com>, <www-ws-arch@w3.org>
Message-ID: <PEEBJKKCFNCENDPJDEMIOEFDDEAA.martin.chapman@oracle.com>

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 14:54:56 GMT

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