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Re: [comment] Formal Semantics, Section 4.3

From: Stasinos Konstantopoulos <konstant@iit.demokritos.gr>
Date: Wed, 29 Apr 2009 12:34:28 +0300
To: Michael Schneider <schneid@fzi.de>
Cc: public-powderwg@w3.org
Message-ID: <20090429093428.GF10597@iit.demokritos.gr>
Michael, hi.

Thank you for reviewing the POWDER formal doc.

> 1) You write /sss^xsd:string/. It should be "^^". This error exists
> several times in the document.

This will be fixed in the next draft, thank you for spotting this.

> 2) I don't think that the semantic condition for wdrs:matchesregex
> is correct, or, at least, I do not understand it.

The basic premise of POWDER is that it is useful to be able to assign
properties to resources based on their name alone and, furthermore,
that POWDER statements can be made about whole sub-spaces of the space
of URI references regardless of whether these sub-spaces contain any
resources.

I believe that this clarifies that we are in total agreement about the
fourth point in your email: it is not our intention to assign
properties to the literal values themselves but to abstract
resources. I shall now proceed to respond to the first three points,
hopefully clarifying how the POWDER extension realizes this.

> I would expect
> that
>
>   < x , reg > in IEXT(I(wdrs:matchesregex))
>
> is meant to hold, if there is an IRI u in the vocabulary V of the
> interpretation I, such that I(u) = x, and the string representation
> of u matches the regular expression reg.

This is, indeed, the intuition that we are formalizing. Unfortunately
we cannot state this quite so simply as "uuu" would then at the same
time be something that can be matched against a regexp (that is,
a string) and something that can be an argument to IS (that is,
a uri ref). So we need two things (a string and a URI ref) that are in  
1:1 correspondance.

The "equivalence relation" chosen as "bridge" is the one of Sect 5.1
of RDF Concepts [1] which provides a 1:1 mapping between strings
and rdf:XMLLiteralS. rdf:XMLLiteralS have the property of being
interpreted in a value space that is disjoint from literal strings
but being able to represent URI refs, so that the IS branch of
the definition of I [2] is applied whenever uuu is a valid
URIref (I see no restriction in RDF Semantics making URIrefs
and rdf:XMLLiteralS disjoint).

I hope this clarifies things.

Best,
Stasinos

[1] http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-XMLLiteral
[2] http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#gddenot
Received on Wednesday, 29 April 2009 09:37:33 GMT

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