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RE: Common RDF parser bug?

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Mon, 21 Jan 2002 12:02:46 -0000
To: "David Allsopp" <d.allsopp@signal.qinetiq.com>, <www-rdf-interest@w3.org>
Message-ID: <JAEBJCLMIFLKLOJGMELDGEMNCCAA.jjc@hplb.hpl.hp.com>

> > >
> > > I think the text from M&S is simply expressing a cardinality
> > > constraint, part of the M&S (informal) ontology.  Therefor this
> > > constraint should be handled when/if other ontology information is
> > > handled, and not in the RDF parser.
> >
> > Hear, hear.
> >
> > ARP explicitly does not do any schema validation.
> >
> > I will *not* be adding this as a defect to ARP's bugzilla.
>
> This does mean that anyone using an RDF parser to load an RDF-XML
> document has no guarantee that the RDF is valid. It will certainly seem
> counterintuitive to RDF newcomers that a conformant RDF parser will
> allow invalid RDF.
>
> It also seems from the replies that different approaches to such invalid
> RDF will occur; some people may attempt to infer equivalences, as Sandro
> suggests, but others could equally well reject the RDF as invalid after
> detecting the wrong number of properties. Which approach is _correct_?
> If there is more than one 'correct' approach, then the meaning of that
> piece of RDF is ambiguous. I think this needs clarifying.
>


On the basis of the new work coming out of the WG I would assert the
following:

Given an RDFS schema, we can take an arbitrary (i.e. schema invalid) RDF
graph and find a smallest supergraph that is RDFS valid. This is its schema
closure.

Thus every RDF-valid document is RDFS-valid.

Cardinality constraints cannot be expressed in RDFS. Domain constraints end
up implying that the subject of rdf:subject is a Statement.

The cardinality constraint in question requires a higher level ontology
language (such as DAML+OIL) to express it. I do not think an RDF (or RDFS)
processor should attempt to validate such constraints. Hence, a system that
offers such validation, should IMO, make it optional and clear to the user
that this is an additional validation over-and-above the standard RDF
validation.

Jeremy
Received on Monday, 21 January 2002 07:02:22 GMT

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