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Re: Presentation Syntax - why?

From: Dan Connolly <connolly@w3.org>
Date: 17 Jun 2003 13:51:04 -0500
To: Jim Hendler <hendler@cs.umd.edu>
Cc: danny666@virgilio.it, www-rdf-logic@w3.org
Message-Id: <1055875863.8713.240.camel@dirk.dm93.org>

On Tue, 2003-06-17 at 07:59, Jim Hendler wrote:
> [Please note, this message is in reply to one from Danny Ayers that
> was posted to public-webont-comments -- his message is included below
> -- I have moved it here to avoid confusion with Last Call comment
> replies on the public-comments list]
> At 11:47 AM +0200 6/17/03, Danny Ayers wrote:

> >
> >The impression this gives is that AS&S has in large part been
> constructed as
> >an entirely new language, with the RDF(S) considerations being
> retrofitted
> >late in the day. How much truth there is in this isn't really
> important,
> >what is important is that the roadmap has become smudged.

The working group is a mix of contributors; each has their
own roadmap. To the extent that there is a shared roadmap,
it is the charter...

 "The language will use the XML syntax and datatypes wherever possible,
and will be designed for maximum compatibility with XML and RDF language
  -- http://www.w3.org/2001/sw/WebOnt/charter#L778

The question of how much XML and how much RDF has been a matter of
considerable discussion. The WG didn't commit to very much
in the requirements document...

  "The language should have an XML serialization syntax."
  -- http://www.w3.org/TR/webont-req/#section-requirements

but by the 2nd face-to-face meeting, the issue had been discussed
enough that some decisions were made, including...

"RESOLUTION: The exchange language for OWL is RDF/XML 

RESOLUTION: We intend to produce non-normative presentation syntaxes and
their mapping to the exchange syntax"

The presentation syntax has been in development all along since then,
but at a lower priority than the exchange syntax. We only just
finished the process of making it a W3C technical report, after we
had released several drafts of the specfication of the exchange

That might look like a "strange crystal that has just appeared" from
where you sit, but I hope you can see that it was just a matter
of priorities about what to release when.

> >I believe significant clarification is required around certain
> issues, in
> >particular those that lead to the Presentation Syntax. It appears
> that this
> >is a concrete representation of the AS&S, but for what purpose?

I'm pretty ambivalent about this XML presentation syntax; I tend
to use N3 for that...

But I've picked up a few bits of motivation for it along the way:

 * you can use XML schema tools to validate documents that use
  this syntax before you convert them to RDF/XML. Finding typos
  in RDF/XML documents can be a pain. You write <soc:Preson>
  and RDF tools just say "oh goodie; a new class I've never
  seen before. Tell me all about it." but (with a few noteable
  exceptions such as the DAML validator) they don't say
  "you probably meant <soc:Person>" or anything like that.

 * Some folks asked about stream-oriented processing for OWL;
 with RDF/XML, you pretty much can't get around a need to
 keep all the triples in memory for the whole parse. With
 the OWL DL structures, I gather you can throw some bits
 away as you go.

>  If the
> >underlying model used by the AS&S is compatible with the RDF
> graph/triples
> >model, then why not use RDF/XML?

For interchange, we are using RDF/XML.

For folks that like to see the XML syntax more closely match
the concepts in the ontology, this is an alternative that
can be mapped to RDF/XML.

>  Or is there such an air gap between the RDF
> >and OWL layers, that the OWL can fly free with it's own model, syntax
> and
> >serialization?

I suppose time will tell.

> >
> >On a practical level, the question is simple if a developer wishes to
> build
> >a Semantic Web application, where do they start?

I hope they start with the interesting bits of their application.

If they want to interchange, they better support RDF/XML.

>  If they start with RDF now,
> >will they need a rework to be able to include OWL features without
> the
> >struggle of [3]?

I don't think so. I think using horn rules with RDF triples is
pretty straightforward.

>  Or if they start with OWL AS&S will they lose the
> >compatibility with existing RDF data without building tools to carry
> out the
> >transformations of [2]?

Yes, I think so. But other folks think otherwise, and their
stuff seems to work too.

> >
> >I realise this is relatively early days for OWL, it just seems from
> what's
> >being delivered that sometimes there are triples being asserted that
> are
> >dark for anyone outside of the WG.
> >
> >Cheers,
> >Danny.
> >
> >[1] http://www.w3.org/TR/2003/NOTE-owl-xmlsyntax-20030611/
> >
> >[2]
> http://www.w3.org/TR/2003/WD-owl-semantics-20030331/mapping.html#4.1
> >
> >[3] http://wonderweb.semanticweb.org/owl/parsing.shtml

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 17 June 2003 14:50:41 GMT

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