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Re: Plain literals and xsd:string

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 20 Apr 2011 18:17:09 +0100
Message-ID: <4DAF1515.4030407@epimorphics.com>
To: Axel Polleres <axel.polleres@deri.org>
CC: public-rdf-dawg@w3.org


On 20/04/11 17:57, Axel Polleres wrote:
> hmmmmmm, potential effects of RDF decisions on Update or Query at this stage worry me... is there a way we can get around such effects
> easily without just ignoring the movements in the RDF WG?

Rather hard to get round, IMO:

"""
Recommend that systems silently convert xs:string data to plain literals
"""

and a SPARQL engine isa system.  So we need to consider it even if we 
find it can be argued for no effect. Ignoring is not really viable.

I haven't looked at "RDF Entailment Regime" and "RDFS Entailment Regime".

xsd:string/simple literal is xsd 1a/1b in "7.4 Datatype Entailment 
Rules" of http://www.w3.org/TR/rdf-mt/.  Don't think it's mentioned 
anywhere else.

Doing it right might be modifying rq25.xml#BGPsparql but I really hope 
we don't have to.  I haven't had space to think about it but it does 
need checking.  Maybe converting in parsing and/or expression evaluation 
is enough.

On the upside, it makes nice, but tricky-in-the-detail, optimization of 
filters/patterns with string work.

	Andy

> Axel
>
> On 20 Apr 2011, at 09:47, Andy Seaborne wrote:
>
>>
>>
>> On 19/04/11 23:17, Steve Harris wrote:
>>> Hi all,
>>>
>>> The RDF WG intends to recommend that xsd:strings be silently
>>> converted to RDF plain literals internally. See Resolution 1 in
>>> http://www.w3.org/2011/rdf-wg/meeting/2011-04-13.
>>>
>>> This would have some impact on SPARQL deployments, as we go to some
>>> lengths in a few places to preserve the differences. I'm not sure it
>>> should necessarily affect the wording of any of the SPARQL texts, but
>>> it's probably worth bearing in mind. It could be that we can simplify
>>> some wording, but we should take care not to become dependent on a
>>> new RDF rec. for publication.
>>>
>>> - Steve
>>>
>>
>> What should update do?
>>
>> INSERT DATA { :s :p "foo"^^xsd:string }
>>
>>
>> It affects query.  BGP matching is simple entailment.
>> The wording must change there surely?
>>
>> Either that or
>>
>> SELECT * { ?s ?p "foo"^^xsd:string }
>>
>> will stop matching on data now converted to "foo" without a software change to the query engine.
>>
>> Existing databases + new software will see a change.
>>
>> In my experience, it is OWL tools that will be affected as they like to use xsd:string in RDF for ontologies.
>>
>> 	Andy
>>
>>
>
Received on Wednesday, 20 April 2011 17:17:36 GMT

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