RE: ONT RE: Data Models, Ontologies, Logic
Dear Jim,
You are confusing the language with what is said.
See comments below.
Matthew West
Principal Consultant
Shell Information Technology International Limited
Shell Centre, London SE1 7NA, United Kingdom
Tel: +44 20 7934 4490 Other Tel: +44 7796 336538
Email: matthew.r.west@is.shell.com
Internet: http://www.shell.com
> -----Original Message-----
> From: Jim Farrugia [mailto:jim@spatial.maine.edu]
> Sent: 28 May 2002 22:12
> To: West, Matthew R SITI-ITPSIE
> Cc: Ontology
> Subject: Re: ONT RE: Data Models, Ontologies, Logic
>
>
> Matthew,
>
> Just a few brief comments below.
>
> Oh, and apologies for the strange formatting - I tried to line things
> up in my mail editor, apparently without success. :-(
>
>
> Jim
>
> ---------------------------------------------------------------------
>
> JA - Jon Awbrey
> JF = Jim Farrugia
> MW = Matthew West
>
> MW: > Dear Jim,
> >
> > The best definition I know of "data model" is "the structure and
> > meaning of data". This is some distance from the ones you offer
> > below. See below for specific comments.
> ...
>
> JF:
> > >
> ---------------------------------------------------------------------
> > >
> > > "A data model is an abstract, self-contained,
> logical definition
> > > of the objects, operators, and so forth, that together
> > > constitute
> > > the abstract machine with which users interact. The
> > > objects allow
> > > us to model the structure of the data. The operators
> > > allow us to model
> > > its behavior."
> > >
> > > Source: An Introduction to Database Systems, Seventh Edition
> > > by C. J. Date. Addison Wesley Longmann,
> 2000, p. 14.
> >
>
>
> > MW: This seems to be how data is represented and processed,
> rather than
> > anything to do with a data model (aka entity-relationship model).
>
> JF: I would agree that the above definition seems to deal with how
> data are represented. It doesn't seem to me, though, that it
> deals with how
> data are processed, if you mean processed by an actual implementation.
MW: This is how I interpret operators and abstract machine.
>
> (In the same book, a few lines below the definition quoted above, is:
> "An implementation of a given data model is a physical
> realization on a
> real machine of the components of the abstract machine that together
> constitute the model.")
>
> I don't mean to suggest that Date's definition is gospel. But he is a
> significant author in database-land, and his way of defining
> the phrase "data models" is probably at least worth considering.
MW: Two points.
1. Date is significant at the "language" level. I have never seen a large
schema definition with his name on it. This is like the difference between
being expert at FOL and expert at metaphysics.
2. Terms get meaning by usage, not definition. At most he is saying how he
is using the term in this context. Don't expect anyone in database
development
land to have this understanding of the term.
>
> Also, I would like to suggest that maybe Matthew's "structure
> and meaning of
> data" really does show up in Date's definition, in the following ways.
>
> Matthew's definition deals with the structure and meaning of data.
> Perhaps one could sensibly claim that the definitions of objects and
> operators (from Date's definition) are a representation that
> allows one to
> model the structure of data, maybe something like the way
> that molded clay
> represents and models a chair?
> (Is it possible to model the structure of data without
> representations?)
MW: Quite. Date is talking about the language. I am talking about what is
said in the language. Therefore they are nto the same thing, but there is
a relationship.
>
> And perhaps the meaning of the data is gotten at, at least
> partially, by
> the operations that can be defined on that data.
>
> I'm just guessing here, and trying to see if this way of understanding
> Date's definition makes sense to Matthew.
>
> For my part, I'd be happy to see Matthew and Jon more or less
> agree on a
> definition that suits them, or come to feel that they each
> know what the
> other means by "data model."
MW: It is just a matter of understanding that there are different usages,
and who uses them for what purpose.
>
> I'm more interested in following these ideas back and forth
> to see what
> may come of this discussion than in trying to foist on you an
> inappropriate
> definition.
>
> I'll leave comments on the Vianu article for later.
>
>
> Jim
>
>