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Re: Ill-typed vs. inconsistent?

From: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
Date: Wed, 14 Nov 2012 21:41:12 +0100
Message-ID: <CA+OuRR8neO=i5rrRcBoC6kVODKgLNnPEbP4aZ=+rsjzeW53H-g@mail.gmail.com>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Cc: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>

On Wed, Nov 14, 2012 at 3:48 PM, Antoine Zimmermann <
antoine.zimmermann@emse.fr> wrote:

> Le 14/11/2012 11:19, Pierre-Antoine Champin a écrit :
> > Pat,
> >
> > On Wed, Nov 14, 2012 at 8:16 AM, Pat Hayes<phayes@ihmc.us>  wrote:
> >
> >> What I still don't follow is, why anyone who understands what an
> >> inconsistency is, would even form the idea that an ill-typed literal
> would
> >> be an inconsistency. It's not the distinction that needs explaining,
> it's
> >> why anyone would treat them as similar in the first place.
>  Illformedness
> >> is not even in the same category as an inconsistency. Literals aren't
> true
> >> or false by themselves.
> >>
> >
> > I think the divergence of opinion comes from the fact that
> >
> > * you see typed literals merely as terms (which, strictly speaking, they
> > are), and a term can not be False; it just denotes something ;
> >
> > * others (at least myself!) see a little more in them, namely: an
> implicit
> > assertion that the denoted thing is indeed in the value space of the
> > datatype.
> >
> > If we decide to bite that bullet, then this could be endorsed in the
> > semantic condition for a *graph*:
> >
> >    if E is a ground RDF graph then I(E) = false if I(E') = false for some
> > triple E' in E,
> >    or if I(E') is not in LV for some typed literal E' in V,
> >    otherwise I(E) =true.
> Ouch. I don't like the fact that the notion of type comes in at the
> level of ground-graph simple entailment.

I don't see how my proposal above makes the notion of type more present
than it was before:
* typed literals are a subset of V, they were already there
* LV is a distinguished subset of IR in *all* interpretation, it was
already there.

I don't believe (nor intend) that the proposal above changes the result of
simple entailment.
The only change is that, in order to satisfy the following graph:

  :a :b "foo"^^xsd:integer .

an interpretation will have to verify

  IL("foo"^^xsd:integer) is in LV

As nothing, in simple entailment, can constrain LV in any way,
nothing prevents a graph consistent with the current condition to have a
satisfying interpretation that meets the condition I propose.

On the other hand, under XSD-entailment, as "foo" is not a valid lexical
form for xsd:integer,
the semantic conditions for datatypes impose to every interpretation that

  IL("foo"^^xsd:integer) is not in LV

so no XSD-interpretation can satisfy the graph above under the condition I

Again, what I'm trying to model is the intuition that any typed literal is
claiming that its lexical form is indeed a lexical value of its datatype
(in rdf-mt parlance: they denote something in LV). This claim is neutral in
simple-entailment, where datatypes have no special meaning (LV is not
constrained). It has some impact in D-entailment (reflected in rdf-mt by
the semantic conditions for datatypes that constraing what can and cannot
be in LV).

Or do you object to this intuition? I had the impression that your proposal
was going that way too...

The more I think of this issue, the more I believe that ill-typed
> literals should be a syntax error. An application that supports a
> datatype should reject RDF graphs that do not write literals of that
> type properly.

That can work of course.
But that makes RDF+XSD a sublanguage of RDF, just like OWL-DL is.
Worse, that makes RDF+D (with D any set of datatypes) a different
Makes me feel uneasy.


> Note that in OWL 2 Structural Specification and Functional Style Syntax,
> it is required that:
> "The lexical form of each literal occurring in an OWL 2 DL ontology MUST
> belong to the lexical space of the literal's datatype."
> cf. Section 5.7 http://www.w3.org/TR/owl2-syntax/#Literals.
> AZ
> > The first line (from the original definition) accounts for everything
> > asserted explicitly in a triple,
> > while the second line (which I added) accounts for those "implicit"
> > assertions carried by typed literals.
> >
> > Do you think it's a clean way to do it? Or do you consider it as just
> > another "trick" ? :-)
> >
> >    pa
> >
> --
> Antoine Zimmermann
> ISCOD / LSTI - Institut Henri Fayol
> École Nationale Supérieure des Mines de Saint-Étienne
> 158 cours Fauriel
> 42023 Saint-Étienne Cedex 2
> France
> Tél:+33(0)4 77 42 66 03
> Fax:+33(0)4 77 42 66 66
> http://zimmer.aprilfoolsreview.com/
Received on Wednesday, 14 November 2012 20:41:46 UTC

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