[sc34wg3] Topic Maps land and SAM land

[Graham Moore]

Hi,=20

Heres my pitch of the model, meta model levels. Its based on my =
understanding of the MOF and OMG layers:

Metametamodel - unclear, some set of concepts to which we subscribe to.=20

Metamodel - the language used to define a model e.g. UML, TopicMaps, =
XML, XML Schema

Model - the definition of classes and relationhsip types, uses UML and =
TopicMaps examples are DTD instance, XML Schema instance.=20

Instance Data - the instatiation of objects and/or topics/ associations. =
These are defined in terms of the Model. i.e. in java object instances =
of a class, in topicmaps Topics of a given type.

Using this definition, both the RM and SAM are metamodels. They are =
expressively different. They promote some different ideas, but they have =
a lot of commonality. In the same way that there is a commonality =
between TopicMaps and UML.

However, and I've said this before...

That the SAM is a refinement of the RM. It is an abstraction that holds =
true to all the principles of the SAM. But as with all abstractions it =
has a purpose. That purpose is to expose the core conceptual parts of =
TopicMaps while hiding some aspects as well.

I've also said before and would like some feedback, that we say that=20

SAM -> RM -> SAM (is a loss less round trip)

RM -> SAM -> RM (is a partial loss scenario)

I think we should embrace this approach and say this is how it works, =
this is how its designed to work.

There is no 1-1 loss less, two way trip from RM to SAM and back. But =
this doesnt mean we dont have a two part cohesive standard.

cheers

graham



-----Original Message-----
From: Sam Hunting [mailto:shunting@etopicality.com]
Sent: 14 February 2003 18:16
To: sc34wg3@isotopicmaps.org
Subject: Re: [sc34wg3] Topic Maps land and SAM land


Martin:

Thanks. I just wanted something to mull over (besides the original John
Sowa quotations at:

http://mars.virtual-earth.de/pipermail/cg/2001q3/003835.html ("I have
never been happy with the notion of 'data model'...") and at
http://mars.virtual-earth.de/pipermail/cg/2001q3/003844.html ("there is =
no
clear notion of a data model"))

> > of "metamodel" has gone unanswered as well. Of course, maybe the =
word is
> > only there for marketing purposes, so I shouldn't concern myself =
with it.
>=20
> Try the following from Table 2.1 of the OMG Unified Modelling =
Language:
>=20
> Metamodel: Defines the language for specifying a model
>=20
> or the definition given in the OMG Modeling Glossary in Annex B of the
> specification:
>=20
> "A model that defines the language for expressing a model."
>=20
> (I prefer the first as the second is circular.)

> In fact UML also defines metamodel as "An instance of a =
meta-metamodel"
> where a meta-metamodel is defined as "The infrastructure for a =
metamodelling
> domain" and defines a model as "Describes a language to define an
> information domain".
>=20
> Whether or not you consider the use of the term metamodel within UML =
(which
> is littered with the term) as an "agreed-upon definition" is up to =
you.

Well, it seems there are three (one of which is circular) so there are =
two
available to us. Which one do we use? Unless, of course, we have a =
fourth
definition. Or indeed if the term is just in the text for marketing
purposes and I don't have to obsess about it. In the former case, I =
guess
it's not an issue, since it would be subsumed under the larger task of
writing the glossary for the SAM. In the latter case, it isn't an issue
because "data model" just becomes a phrase that achieves a certain =
comfort
level for an audience (as Sowa puts it), rather than a term -- not that
there's anything wrong with that.

Martin -- "Be open to the possibility that being is!"=20



> Martin Bryan
> IS-Thought: Thinkers for the Information Society
> 29 Oldbury Orchard, Churchdown, Glos. GL3 2PU, UK
> Phone/Fax: 01452 714029 E-mail: martin@is-thought.co.uk
>=20
> Thought of the week:
> Is "being" necessary? Won't "known as" suffice?
>=20
>=20
> _______________________________________________
> sc34wg3 mailing list
> sc34wg3@isotopicmaps.org
> http://www.isotopicmaps.org/mailman/listinfo/sc34wg3
>=20

Sam Hunting
eTopicality, Inc.

-------------------------------------------------------------------------=
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Co-Editor, ISO Reference Model for Topic Maps=20

Topic map consulting and training: www.etopicality.com
Free open source topic map tools:  www.gooseworks.org

XML Topic Maps: Creating and Using Topic Maps for the Web.
Addison-Wesley, ISBN 0-201-74960-2.
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