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Re: RDF, RDFS and DAML+OIL benifits over XML (fwd)

From: Libby Miller <Libby.Miller@bristol.ac.uk>
Date: Wed, 6 Nov 2002 13:05:30 +0000 (GMT)
To: Pedro Assis in Oporto <passis@dee.isep.ipp.pt>
cc: www-rdf-interest@w3.org
Message-ID: <Pine.GSO.4.44.0211061232160.23685-100000@mail.ilrt.bris.ac.uk>

Thanks Pedro - this gives me a chance to try out a frequently asked
question answer.

Below is paraphrased from an exchange at a workshop at DC2002[1] which
will be expanded into an FAQ for RDF for the SWAD-Europe project [2].
Eric Miller and Dan Brickley provided the ideas - but paraphrasing
errors may have crept in which are mine. If it's not good enough, we
need to persuade you! let us know.

My personal feelings are represented in [3] - if you ever need to reuse
or share - use RDF over plain XML.

Q: RDF and XML - which one do I choose?

A: XML is a very powerful language for describing heirarchical things.
It defines what goes into a document. For 'known target' interactions
XML works very well.

However, XML encodes all the information about what any particular
element means and how it relates to any other element in human-readable
terms: it doesn't mean anything to a machine unless the machine already
knows about it.



For example, if you or I read the above we might think that '<name>' was
related to the tag above it '<person>' in that it was an actual
person's given name; and we would realize that a W3Cprofiledate was a
specific type of iso8601date. But structurally, and
syntactically, they look very similar in XML even though the
relationship between each pair of elements means something completely
different. Unless machines pre-co-ordinate, machine understanding of
these relationships is very hard because of the implicit, not
explicit semantics in ordinary XML. RDF, through schemas and extensions
like DAML+oil or OWL can provide machine-readable semantics, even when
there is no pre-coordination.

There is also a difference in the perspectives of RDF and XML: XML is
about documents; RDF is about the world. XML is about the number of
elements of certain types, their attributes and ordering, and the sorts
of text that can appear in datatypes, while RDF is about things in the
world -  people who have names, create documents, have friends. RDF
is about real things in the world not the documents that describe them.

[1] http://www.bncf.net/dc2002/
[2] http://www.w3.org/2001/sw/Europe/
[3] http://www.ilrt.bris.ac.uk/discovery/2002/04/query/

Dr Libby Miller
ILRT Semantic Web Coordinator

On Wed, 6 Nov 2002, Pedro Assis in Oporto wrote:

> Hi,
> I've read several W3C and DAML docs about RDF, RDFS and DAML (DAML+OIL),
> and their role in the Semantic Web project, but I'm still puzzle by the
> answers given to the basic question: "why use RDF-based technology rather
> than only XML-based?" If one use an OO modeling (expressive issue is
> address here) to describe the knowledge related to the target domain,
> translating the resulting schemata to XML, shouldn't the XML output
> address the same functionality as a RDF-based solution? Is it a mater of
> logic/inference capability?
> Regards,
> --
> Pedro
> passis@dee.isep.ipp.pt | Tel. +351 22 8340500 Ext. 1712
Received on Wednesday, 6 November 2002 08:07:04 UTC

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