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Re: Comment on rdf:parseType="Collection"

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Date: Thu, 20 Feb 2003 08:46:15 +0000
To: Jim Hendler <hendler@cs.umd.edu>
cc: www-rdf-comments@w3.org
Message-ID: <766.1045730775@hoth.ilrt.bris.ac.uk>

Brian: please accept this as a last call issue for RDF Core on the
RDF/XML Syntax specification 2002-01-23

>>>Jim Hendler said:
> The RDF Core Working Group documents (particularly [1]) reflect a 
> decision that rdf:parsetype="collection" must be a list if RDF node 
> elements.  I believe the RDF Core WG is making a mistake by 
> prohibiting this from being a list of literals, and to the best of my 
> ability to deduce, there is no technical reason why a list of 
> literals could not be supported.

I'll demonstrate the technical issues with your example, below.

> This decision has terrible ramifications for languages built on top 
> of RDF (like OWL) which thus must use extremely ugly constructs for 
> lists of literals (in fact, constructing the entire list using List, 
> first, and rest).  For example, a natural thing to express in OWL (or 
> RDFS for that matter) might be that the list of permissible scores in 
> a game of tennis are 0, 15, 30, and 40.  However, instead of the 
> construct
> <owl:oneOf rdf:parsetype="collection">
>   <score rdf:datatype="xsd:integer">0</score>
>   <score rdf:datatype="xsd:integer">15</score>
>   <score rdf:datatype="xsd:integer">30</score>
>   <score rdf:datatype="xsd:integer">40</score>
> </owl:oneOf>
> we must instead

(minor error rdf:parseType="Collection")

I'll complete your example to make it a full rdf/xml document,
such that it could be sent to the W3C's RDF Validator, although it
won't work since it doesn't support rdf:datatype at this date.

(Aside, you are using qnames inside the rdf:datatype which is a minor
error, I'm also correcting with entities).

<?xml version="1.0"?>
  <!ENTITY xsd 'http://www.w3.org/2000/10/XMLSchema#'>
  <!ENTITY rdf 'http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   <rdf:Description rdf:about="http://example.org/">
             <rdf:first rdf:datatype="&xsd;integer">0</rdf:first>
                 <rdf:first rdf:datatype="&xsd;integer">15</rdf:first>
                     <rdf:first rdf:datatype="&xsd;integer">30</rdf:first>
                         <rdf:first rdf:datatype="&xsd;integer">40</rdf:first>
                         <rdf:rest rdf:resource="&rdf;nil" />

So these potentially are the triples that OWL wants to use
(made from my Rapper parser):

_:genid1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> .
_:genid1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "0"^^<http://www.w3.org/2000/10/XMLSchema#integer> .
_:genid2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> .
_:genid2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "15"^^<http://www.w3.org/2000/10/XMLSchema#integer> .
_:genid3 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> .
_:genid3 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "30"^^<http://www.w3.org/2000/10/XMLSchema#integer> .
_:genid4 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> .
_:genid4 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "40"^^<http://www.w3.org/2000/10/XMLSchema#integer> .
_:genid4 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> .
_:genid3 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:genid4 .
_:genid2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:genid3 .
_:genid1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:genid2 .
<http://example.org/> <http://www.w3.org/2002/07/owl#oneOf> _:genid1 .

and this is thus the RDF you want out of it.

Your suggestion:

 <owl:oneOf rdf:parseType="Collection">
   <score rdf:datatype="xsd:integer">0</score>
   <score rdf:datatype="xsd:integer">15</score>
   <score rdf:datatype="xsd:integer">30</score>
   <score rdf:datatype="xsd:integer">40</score>

doesn't seem to relate to the triples or the expanded RDF/XML at all.
The 'score' item appears nowhere in the N-Triples.  Is this a crucial

The historical background to rdf:parseType="Collection" is that it
was designed to copy how DAML lists work
(rdf:parseType="daml:Collection") and this list of literals short cut
was never in that design, which was presented only in the form of an
example.  DAML lists only ever used resource nodes (URIs) as the list
contents so that limitation was carried forward.  We extended it to
include bnodes since the contained node element.

So it would be a new requirement to have literals objects of the
rdf:first property which has not, to my knowledge, previously been
asked of the RDF Core working group.

The technical issue of how to invent a new way to allow both the node
elements and literal objects as the value of the rdf:first statement
is something the WG can consider.  My immediate reaction is that it
would require a new piece of rdf/xml syntax.

> I believe the ability to express a collection of datatype values is a 
> very important one, and believe it is a mistake for RDF Core to put 
> this restriction on the use of rdf:parsetype="collection" without a 
> stronger motivation than I can find in the current LC documents.
>   thanks
>   Jim Hendler
>   AC Member, MIND Laboratory
> p.s. Please note this is an individual comment raised as AC member, 
> not a consensus comment from the web ontology working group nor does 
> it necessarily represent the opinion of any other group or 
> organization with which I am affiliated.  I also apologize if this 
> issue has been brought up before - if it has, just consider this a +1 
> for the objection.
> [1] 
> http://www.w3.org/TR/rdf-syntax-grammar/#section-Syntax-parsetype-Collection
> -- 
> Professor James Hendler				  hendler@cs.umd.edu
> Director, Semantic Web and Agent Technologies	  301-405-2696
> Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
> Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
> http://www.cs.umd.edu/users/hendler

Thanks for the comment Jim.

Received on Thursday, 20 February 2003 03:46:55 UTC

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