[ontolog-forum] [Fwd: Re: When are XML Schema and Ontologies Alternativ

[Leo Obrst <lobrst@xxxxxxxxx>]

FYI: Mike, this forum is now named ontolog-forum@xxxxxxxx -- per your message
and my reply below. I thought there was an alias, but I haven't seen it
show up.

Leo

-------- Original Message --------

Subject:	Re: When are XML Schema and Ontologies Alternatives? $xmls
Date:	Fri, 07 Mar 2003 07:28:57 -0500
From:	Leo Obrst <lobrst@xxxxxxxxx>
Organization:	The MITRE Corporation
To:	"Uschold, Michael F" <michael.f.uschold@xxxxxxxxxx>
CC:	"Frank van Harmelen (E-mail)" <Frank.van.Harmelen@xxxxxxxx>,"Peter Patel-Schneider (E-mail)" <pfps@xxxxxxxxxxxxxxxxxxxxxx>,ht@xxxxxxxxxxxxxxx,"Jerome Simeon (E-mail)" <simeon@xxxxxxxxxxxxxxxxxxxxxx>,"DLU Ontolog (E-mail)" <ontolog@xxxxxxxxxxxxxxx>,erdmann@xxxxxxxxxxxxxxxxxxxxx,"Rudi Studeri (E-mail)" <studer@xxxxxxxxxxxxxxxxxxxxx>,"Jones, Janet L" <janet.l.jones@xxxxxxxxxx>,"Moody, Laura L" <laura.l.moody@xxxxxxxxxx>,"Jones, David H" <david.h.jones@xxxxxxxxxx>,"Thompson, John A" <john.a.thompson@xxxxxxxxxx>,"Murray, Paul" <paul.murray@xxxxxxxxxxxxxx>
References:	<823043AB1B52784D97754D186877B6CF01E7514C@xxxxxxxxxxxxxxxxxxxxxxxxxxx>

We've recently been discussing a variant of this question internally (in MITRE) across two communities, the database and the ontology folks. I.e., data modeling vs. ontology engineering. I think our point of departure was the SIGMOD paper from last year:

Data Modelling versus Ontology Engineering. P. Spyns, R. Meersman, M. Jarrar, Special Section on Semantic Web and Data Management, V. 32:4, December, 2002.  http://www.acm.org/sigmod/record/issues/0212/SPECIAL/2.Meersman.pdf.

Note the above requires a login account.

I think the short answer is that database schemas and XML Schema are a way of structuring data/document collections for some generally local purpose, e.g., to satisfy an application (or set of applications) or, in the case of XML Schema, for some generally local exchange of documents/messages.  So, in general, schemas are focused on structure rather than the meaning of constructs that define that structure. And ontologies address a more "global" view, in terms of real world semantics.

*However, we all know that structure is the mother of meaning too, that in fact no semantics is possible without it, and that the formal objects on the "semantics" side to which the syntax/structures map (in model-theoretic semantics via an interpretation function) and which we take to "stand in" for the real/possible world entities whose semantics we want to capture, are themselves structured (probably because we want those objects to have certain formal properties, ordering relationships, etc.)

That said, maybe the shortest answer is: A constraint in an XML Schema is a constraint on the structure or form of a document, not on the meaning of a real world object as in an ontology.

Leo

"Uschold, Michael F" wrote:

It is not usual for someone to show me an XML shema and say, "Hey, what do you think of my ontology?", or: "Gee, we are using an ontology now, but everyone's using XML, so maybe we should use an XML Schema instead?".   Indeed, some people have the impresson that XML Schema and ontologies** are similar animals and one can use one or the other for a given problem.

Where does this impression come from?

For SOME problems, ontologies and XML Schema seem for all practical purposes, to be alternatives. One can create an ontology and a data set conforming to that ontology, or one could create an XML schema and pass data conforming to that schema. There would be  a clear mapping between classes and attributes in the ontology and elements and attributes in the XML schema.

However, I believe that for MOST problems ontologies and XML schema are not appropriately seen as alternatives, indeed they are quite different animals for quite different purposes, and can be used to good effect together complementing each other.

Can anyone resolve this paradox?  One great way to answer the question is like this:

If properties p1, p2, ... pn  hold for a given situation, then for most practical purposes, XML schema and ontologies can be viewed as alternatives.  This is because <now explain how properties p1-pn make this so, and why when those properties do not hold, the situation changes and how.>.

What are the properties? I would guess that one has to do with the intended purpose of the ontology/schema. Related to this would be inference requirements.

Thanks,
Mike Uschold

** For now, lets say by ontology I mean a simple language like OKBC or even RDFS that one can use Protégé for.

--
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Dr. Leo Obrst  The MITRE Corporation
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