W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > January 2002

Re: RDF datatyping goals (action from teleconference)

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Tue, 15 Jan 2002 12:38:10 +0000
Message-Id: <5.1.0.14.2.20020115121807.00ac5600@joy.songbird.com>
To: Patrick Stickler <patrick.stickler@nokia.com>
Cc: Jeremy Carroll <jjc@hplb.hpl.hp.com>, RDF Core <w3c-rdfcore-wg@w3.org>
At 09:45 AM 1/15/02 +0200, Patrick Stickler wrote:
> > I'll also argue that (a) is semantically equivalent to (b) in the sense
> > that if an RDF graph and any associated schema graphs are merged, the
> > result can be interpreted per (a).
>
>This I don't fully agree with. The typing knowledge defined in the
>schema may have multiple possible interpretations.
>
>The semantics of the rdfs:range 'constraint' (as I see it) is to
>define an implicit union of data types, the members being the objects
>of the rdfs:range, which may be used to

"intersection", not "union" (per WG resolution).

>1. Deduce the type(s) of a non-locally typed literal by examination
>    of those lexical forms in terms of the definition of the lexical
>    space for each type (all types which match are inferred as valid
>    types for the literal). In the case of XML Schema, where type unions
>    are explicitly ordered, this deduction would infer only one type,
>    namely the first to match the lexical form as a valid member of its
>    lexical space.

Maybe.

>2. Constrain the type(s) of a locally typed literal by expecting/requiring
>    that the literal represents a lexical form that is a member of the
>    lexical space of at least one of the union member types.

OK, if by "constrain" I can understand a limitation the interpretations 
that may be considered to be models.

>and I'm sure that other equally valid and useful interpretations exist.

I see nothing here that argues that the meaning of:

    Direct Graph + Schema Graph

should be any different to the meaning of the merge of those graphs.  I.e. 
the same conclusions can be drawn either way.

In the model theory, the meaning of schema statements is defined in terms 
of entailment over a subset of interpretations called RDFS 
interpretations.  And the schema lemma is pretty explicit that the schema 
entailment of some set of graphs is equivalent to the schema-closure of the 
merge.

>Which interpretation is applied is up to the particular application.

I think we really should be steering well away from that:  if different 
applications can draw different conclusions from some graph+schema, then 
where is the basis for interoperable exchange of information in RDF?

#g



------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
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Received on Tuesday, 15 January 2002 08:13:12 EST

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