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RDF collections

From: Graham Klyne <GK@dial.pipex.com>
Date: Fri, 07 Jul 2000 12:40:38 +0100
Message-Id: <4.3.2.7.2.20000707120309.00ab24f0@pop.dial.pipex.com>
To: RDF comments <www-rdf-comments@w3.org>
Cc: CC/PP WG list <w3c-ccpp-wg@w3.org>
Folks,

In our work on CC/PP using RDF, we have come across an issue in designing a 
schema for representing set values using RDF collections.

The desire was to use a new RDF class, ccpp:Set, defined as a subclass of 
rdf:Bag, to be a restricted bag-like container for CC/PP value 
sets.  Unfortunately, because of the way that collections are expressed 
using the RDF syntax, this construct cannot be parsed by a non-schema-aware 
RDF parser, because of the use of <li> elements to represent 'rdf:_n' 
properties.   It is necessary for the parser to be aware that the subject 
resource is an instance of 'rdf:Bag' to apply this transformation ... 
information that is available only through the schema.

I believe that using schema to build rich class structures for application 
domains is a powerful tool for future evolution of RDF applications.  I 
have been promoting the idea that using a rich class structure should not 
impose any additional implementation burden on specific applications, but 
may open the application data to more general use by schema-aware 
applications and tools.  The issue described above is an impediment to 
using rich class structures in this way.

How might this issue be resolved?  Some thoughts:

(a) use rdf:_1, rdf:_2, etc. directly as element names in the XML 
serializatiion of RDF collections.

(b) use rdf:li within the RDF model graph to indicate membership of a 
collection.  For an rdf:Bag this raises the issue of whether the same RDF 
statement (i.e. the same sub-->pred-->obj triple) can appear more than once 
in a model.

(c) have some schema-independent way of indicating that a class is derived 
from an RDF collection class (or a resource is an instance of a collection).

(d) introduce a convention that <rdf:li> elements are mapped to unique, 
sequential 'rdf:_n' properties regardless of the class to which they are 
applied.

...etc.

#g

------------
Graham Klyne
(GK@ACM.ORG)
Received on Monday, 10 July 2000 03:45:41 GMT

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