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Re: [TF-ENT] RDFS entailment regime proposal

From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
Date: Mon, 28 Sep 2009 15:00:33 +0100
Message-ID: <492f2b0b0909280700o67c406e9rbb48794f29bd7aaf@mail.gmail.com>
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
2009/9/28 Seaborne, Andy <andy.seaborne@hp.com>:
>> -----Original Message-----
>> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg-
>> request@w3.org] On Behalf Of Birte Glimm
>> Sent: 24 September 2009 18:31
>> To: SPARQL Working Group
>> Subject: [TF-ENT] RDFS entailment regime proposal
>> Hi all,
>> whoever is interested in RDFS entailment: I would be very happy about
>> comments and suggestions for the RDFS entailment regime as outlined
>> in:
>> http://wiki.webont.org/page/SPARQL/OWL
> The "Illegal Handling" says an error must be raised for illegal graph or query.
> I would very much like to leave this undefined, which includes the possibility of raising an error but leaves the mechanism up to the implementation.
> That is, illegal data or query puts a system outside the spec.  For example, if the graph is illegal (e.g. bad literal lexical form) but the query never touches that part of the graph, then the processor should be free to return something, and not be forces to raise an error which might require touching the whole graph to check it.
> This also arises in query optimization as a BGP might be solved repeated by substitution (index join style) from data elsewhere in the query and the error might only be raised on quite lat eon in query processing but the whole query is required to be an error by the spec.
>        Andy

Well, but under RDFS semantics you have to check consistency first
anyway since an inconsistent graph entails all tuples. Bad lexical
forms are not causing an inconsistency, only when combined with an
assertion that the range of the used property/predicate is
rdfs:Literal or rdf:XMLLiteral. Thus, if you parse a data set and find
a literal that has a bad lexical form, you better check consistency
anyway and after that you know whether your data is legal or not.
Also, if a user asks
SLEECT ?x WHERE { ?x <ex:b> <ex:c> . }
I would expect an error because I wrote SEELCT instead of SELECT and I
should be told that the query is not a legal query. Similarly
SELECT ?x WHERE { ?x <ex:b> <ex:c> <ex:forthInATriple> . }
should give me an error, right?

I can see your point for simple entailment, but for RDFS entailment I
would think that illegal data or query are best treated by an error.


Dr. Birte Glimm, Room 306
Computing Laboratory
Parks Road
United Kingdom
+44 (0)1865 283529
Received on Monday, 28 September 2009 14:01:14 UTC

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