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RE: ISSUE 5.6 - daml:imports as magic syntax

From: Smith, Michael K <michael.smith@eds.com>
Date: Thu, 12 Sep 2002 07:31:39 -0500
Message-ID: <B8E84F4D9F65D411803500508BE32214106BCE0E@USPLM207>
To: Jeff Heflin <heflin@cse.lehigh.edu>
Cc: www-webont-wg@w3.org

The imbedding of rdf:rdf is a good point.  We have not said that imbedding
owl:ontology in an owl:ontology is legal either.  

The most obvious way around it would seem to be the following.  We could
assert that imports clauses are preprocessed and extracted to the top level,
so that we end up with a sequence of ontologies, rather than a set of
recursively imbedded ones.  This combined with XML:Base would still seem
fairly simple. I don't see anything in RDFM&S that would prevent this. 

There are other possibilities.  RDF permits xmlns attributes to appear in
other places besides the RDF:RDF term.  So, on importation we could push
them down to the owl:ontology and delete the rdf:rdf term.

We could also admit that we are writing OWL, and not require an OWL document
to be wrapped in RDF tags.  Since not even RDF requires an RDF:RDF element.
Quoting from 2.2.1: 

  The RDF element is optional if the content can be known to be RDF 
  from the application context.

In which case the owl:ontology tag would be expected to carry the namespace
information.  And we could permit imbedding.  Semantically, this tag is
nearly a no-op (assuming ontologies are not classes or objects.)

- Mike

-----Original Message-----
From: Jeff Heflin [mailto:heflin@cse.lehigh.edu]
Sent: Wednesday, September 11, 2002 4:27 PM
To: Smith, Michael K
Cc: www-webont-wg@w3.org
Subject: Re: ISSUE 5.6 - daml:imports as magic syntax


Mike,

Your XML:Base solution certainly get around the relative URI problem.
But I'm not sure why you don't think it handles the <ontology about="">
problem. That's just another relative URI. However, there is still a
problem:

I don't think the embedded rdf:RDF tags are legal RDF. In RDFM&S Section
2.2.1 it seems that rdf:RDF should only appear at the top-level of a
document. If it is legal, then it would be interpreted as a property of
an Ontology, which doesn't seem right.

Jeff



"Smith, Michael K" wrote:
> 
> Here is what I think is a simple suggestion for an essentially
> syntactic treatment of owl:imports using XML:Base.
> 
> I wrote this note and then finally followed Jonathan's pointer to
> XInclude, which seems like a decent option, except for the requirement
> that a loop be a fatal error.  In distributed ontologies I would
> expect loops to show up.  ???
> 
> As I understand our current draft status, the structure of an OWL
> ontology with an imports clause is,
> 
> <rdf:rdf
>     xmlns     ="#"
>     ... plus other namespace declarations >
>  <owl:ontology about="">
>   ...
>   <owl:imports rdf:resource="http://www.w3.org/foo.owl" />
>   ...
>  </owl:ontology>
> </rdf:rdf>
> 
> (No comment on how odd the RDF:RDF wrapper around all OWL ontologies
> seems.)
> 
> If we consider textually replacing the imports clause with the text of
> the referenced ontology we would get something like:
> 
> <rdf:rdf
>     xmlns     ="#" >
>  <owl:ontology about="">
>   ...
>   <rdf:rdf
>       xmlns     ="#" >
>    <owl:ontology about="">
>     ...
>    </owl:ontology>
>   </rdf:rdf>
>   ...
>  </owl:ontology>
> </rdf:rdf>
> 
> Which has obvious problems, in both the imbedded namespace declaration
> and the imbedded 'about' attribute.
> 
> It would seem that we could solve this using XML:BASE.  Suppose the
> expansion augmented the imported ontology with a base expression that
> referenced the imported document.
> 
> <rdf:rdf
>     xmlns     ="#" >
>  <owl:ontology about="">
>   ...
>   <rdf:rdf
>       xml:base= "http://www.w3.org/foo.owl"
>       xmlns     ="#" >
>    <owl:ontology about="">
>     ...
>    </owl:ontology>
>   </rdf:rdf>
>   ...
>  </owl:ontology>
> </rdf:rdf>
> 
> This should actually work for the namespace component, since the scope
> of the xml:base occurence starts with the rdf:rdf element, and will
> extend until a new base is established or we exit the scope of the
> rdf:rdf tag. (See http://www.w3.org/TR/xmlbase/)
> 
> So, the remaining problem is the imbedded 'about' attribute.  Since we
> get to define what this attribute means, I would think we could define it
> relative to the current base URI.
> 
> Note that this works in the case of multiple, imbedded imports.
> 
> - Mike
> 
> Michael K. Smith, Ph.D., P.E.
> EDS - Austin Innovation Centre
> 98 San Jacinto, #500
> Austin, TX  78701
> 
> * phone: +01-512-404-6683
> * mailto:michael.smith@eds.com
> 
> -----Original Message-----
> From: Dan Connolly [mailto:connolly@w3.org]
> Sent: Tuesday, September 10, 2002 11:28 AM
> To: Jonathan Borden
> Cc: Jeff Heflin; Peter F. "Patel-Schneider; www-webont-wg@w3.org
> Subject: Re: ISSUE 5.6 - daml:imports as magic syntax
> 
> On Mon, 2002-09-09 at 19:40, Jonathan Borden wrote:
> >
> > Peter F. Patel-Schneider wrote:
> > >
> > > A treatment of imports can be done completely syntactically, by
> replacing
> > > imports foo, where foo is a URI (or whatever) by the contents of the
> > > document pointed at by foo.   This is the way I would handle it in the
> > > abstract syntax and direct semantics.
> >
> > hmmm... if we consider that daml:imports is syntactic sugar for XInclude
> > http://www.w3.org/TR/xinclude/ i.e.
> >
> > <xi:include
> >     xmlns:xi="http://www.w3.org/2001/XInclude"
> >     href="foo.daml"
> > />
> >
> > just using XInclude as it is already specified would allow us to prune
> this
> > whole discussion and the issues it raises of special syntax, semantics
> etc.
> 
> Not a bad idea...
> 
> XInclude wouldn't come for free (the RDF/XML spec doesn't say that
> RDF parsers must grok XInclude) but if we're interested in special
> syntax for syntactic inclusion, I'd prefer XInclude syntax, which
> is designed for exactly that purpose, rather than daml:imports,
> which sorta looks like an RDF property but it's sorta unclear
> how to specify that it acts like one.
> 
> --
> Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 12 September 2002 08:31:51 GMT

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