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Re: Proposal for ISSUE-12, string literals

From: Peter Frederick Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 13 May 2011 14:57:21 -0400
Message-ID: <20110513.145721.1960025422108618789.pfps@research.bell-labs.com>
To: <ivan@w3.org>
CC: <richard@cyganiak.de>, <alexhall@revelytix.com>, <phayes@ihmc.us>, <public-rdf-wg@w3.org>
Well this change would indeed invalidate OWL reasoners, but not because
of anything to do with rdf:PlainLiteral.  Instead, the change to the
underlying semantic model of RDF would require changes to everything
that layers on top of (this part of) RDF.

The only rdf:PlainLiteral fly in the above ointment is "plain literals
and rdf:PlainLiterals don't exist", which is qualitatively different
from anything else about RDF.


From: Ivan Herman <ivan@w3.org>
Subject: Re: Proposal for ISSUE-12, string literals
Date: Fri, 13 May 2011 13:48:17 -0500

> I would like to check this line with the OWL and RIF folks. It may
> invalidate OWL reasoners, for example, that use rdf:PlainLiteral. there
> is a slippery slope here; that indeed mean that we would change the very
> concept of datatype maps.
> I have to ask this: is this worth it?
> Ivan
> ----
> Ivan Herman
> Tel:+31 641044153
> http://www.ivan-herman.net

> On 13 May 2011, at 19:42, Richard Cyganiak <richard@cyganiak.de> wrote:
>> On 13 May 2011, at 16:52, Alex Hall wrote:
>>>> I think the sensible way would be:
>>>> 1) every literal has *both* a datatype and a (possibly empty)
> language tag;
>>>> 2) of the built-in datatypes, only xsd:string can have non-empty
> language tags;
>>>> 3) plain literals and rdf:PlainLiterals don't exist;
>>>> 4) "foo" in concrete syntaxes is syntactic sugar for
> "foo"^^xsd:string.
>>>> 5) "foo"@en in concrete syntaxes is syntactic sugar for
> "foo"^^xsd:string@en.
>> ...
>>> The main roadblock that I can see is that a datatype maps a single
> lexical string to a value; you'd have to define a special notion of
> datatyping for xsd:string which is essentially an identity mapping of
> <lexical, lang> pairs.  Otherwise you'd have "chat"^^xsd:string@en and
> "chat"^^xsd:string@fr with the same value, which won't fly.
>> Yes, that's right, RDF Semantics would have to be adapted to ensure
> that "foo"@en and "foo"@fr (which are now syntactic sugar for
> "foo"^^xsd:string@en and "foo"^^xsd:string@fr) are still different. But
> I think that's doable:
>> Let's write "xxx"^^yyy for a typed literal with *empty* language
> tag. Its interpretation is L2V("xxx"), where L2V is the lexical-to-value
> mapping of datatype yyy.
>> Let's write "xxx"^^yyy@zzz for a typed literal with *non-empty*
> language tag. Its interpretation is <L2V("xxx"), zzz>.
>> How exactly to distribute that logic between Simple Entailment and
> D-Entailment requires some thought. You can't remove plain literals from
> RDF without changing a couple lines of RDF Semantics ...
>> This entire proposal breaks backwards compatibility in two ways:
>> 1. The following Turtle file would now contain only one triple instead
> of two:
>>   <a> <b> "foo", "foo"^^xsd:string .
>> This obviously has some serious knock-on effects, for example SPARQL
> stores that have already loaded this file now need to drop a triple,
> which changes the results of many queries.
>> 2. In SPARQL, datatype("foo"@en) would now report xsd:string instead
> of ø. That seems like a good thing to me (it's explainable by saying
> that the language tag is “attached” to the “outside” of the typed
> literal). I believe this is *fairly* unlikely to cause interoperability
> issues with existing queries.
>> Best,
>> Richard
Received on Friday, 13 May 2011 18:58:45 UTC

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