Re: [xtm-wg] A challenge on "the graph"

[Murray Altheim <altheim@eng.sun.com>]

"W. Eliot Kimber" wrote:
> 
> Murray Altheim wrote:
> >
> > Sam Hunting wrote:
> > [...]
> > > [murray]
> > > > We need a data model in order to describe a processing model.
> > >
> > > Please elucidate.
> >
> > Amid all the hairpulling and bloodletting in Austin, the central message
> > *I* pulled from everything was that TMQL and the processing model both
> > need a data model, that is, a formal description of the underlying
> > structure of the various components in a topic map. This can't be UML
> > as this model cannot rely on notes.
> 
> Let me repeat: UML HAS MATHEMATICAL CONSTRAINTS

To be more precise, UML *can have* mathematical constraints.
 
> You can use the OMG-defined object constraint language (OCL) or you can
> use your own languag (John Heintz and I use a slightly modified version
> of Python for this).
> 
> These constraints are specified constraints on classes, attributes,
> methods, etc. For example, in ObjectDomain, the property editor gives
> you a place to type in these constraints.
> 
> These constraints cannot be expressed graphically, any more than prose
> comments can be, but then they can't be expressed graphically in *ANY*
> graphical notation.
> 
> Therefore, lack of mathematical constraint specification *CANNOT BE A
> CRITERIA FOR ELIMINATING THE USE OF UML*. There may be other reasons,
> but this cannot be one of them.

What I was trying to express (perhaps not so clearly as I'd like) is that
I think we're looking for something extremely simple, but formal. While
it is possible to describe a set of constraints (in prose) on a graphical
language, what is really needed here are constraints at all but a formal
modelling method. I'd be happy with circles and arcs if we could find 
one that was in common use, didn't require our reinvention or redefinition
(as is the case with UML, where that is our only option unless we adopt
somebody else's, like ObjectDomain's), itself had a formal definition,
and was clear and easy enough to understand that it wouldn't be readily
misinterpreted by half the planet. 

Perhaps UML is the ticket. Perhaps the XTM data model can be described
formally in UML. As I've said previously, I remain to be convinced. I'd
ideally like to find something that was more specific to graph theory,
try that out and if if doesn't fit, we then know that graphs aren't the 
best way to express topic map concepts. Since we (at least in theory)
have some good graph experts in the room it's at least not a bad start.

Murray

...........................................................................
Murray Altheim, SGML/XML Grease Monkey     <mailto:altheim&#64;eng.sun.com>
XML Technology Center
Sun Microsystems, 1601 Willow Rd., MS UMPK17-102, Menlo Park, CA 94025

      the wood louse sits on a splinter and sings to the rising sap
      ain't it awful how winter lingers in springtimes lap -- archy

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