Re: [office-metadata] RDF datatypes

[Elias Torres <eliast@us.ibm.com>]

John Madden <john.madden@mac.com> wrote on 05/10/2007 11:36:45 AM:

> Hi guys,
>
> I looked a little into the "datatypes in RDF" question. I think the
> answer is in the RDF Abstract Semantics, section 4.3
>
> 4.3 A Note on rdfs:Literal
> Although the semantic conditions on rdfs-interpretations include the
> intuitively sensible condition that ICEXT(I(rdfs:Literal)) must be
> the set LV, there is no way to impose this condition by any RDF
> assertion or inference rule. This limitation is due to the fact that
> RDF does not allow literals to occur in the subject position of a
> triple, so there are severe restrictions on what can be said about
> literals in RDF. Similarly, while properties may be asserted of the class

> rdfs:Literal, none of these can be validly transferred to literals
themselves.
> Note the comment that "...there is no way to impose this condition
> by any RDF assertion or inference rule." What this means, as I take
> it, is that in effect literals (including datatyped literals) are a
> "special feature" of RDF, and their semantics DOES NOT map to any
> "plain-vanilla" RDF model. They have their own special semantics,
> which is explicit (see http://www.w3.org/TR/rdf-mt/#dtype_interp),
> but is not specifiable in RDF.
>
> What this means for us is, that the meaning of m:datatype is NOT
> that it generates any new triples, but rather that is restricts the
> value space of the interpretation of the typed literal to which it
> applies in accordance with http://www.w3.org/TR/rdf-mt/#dtype_interp .
>
> While datatype restriction cannot be expressed as RDF triples,
> nevertheless the RDF spec does provide a standard notational device
> for indicating that such datatype restrictions apply , namely the
> "^^" notation, as in
>
> "125"^^xsd:integer
> "20070101"^^xsd:date
> "3.14159"^^xsd:float
>
> Consequently, when an ODF metadata parser encounters an m:data-type
> attribute, the response of the parser should NOT be to produce any
> additional triples, but SHOULD be to append the appropriate ^^-
> suffix to the literal to which the m:data-type attribute applies
> (which will be either the value of the associated m:data-value
> element; or in the absence of such an element, the value of the
> XMLLiteral that is the child of the xml element carrying the
> datatype restrcition.
>
> Elias, does this sound reasonable?
>
> john

This is a summary of our discussion with Svante yesterday..

<text:p m:about="uri:SvanteS" m:property="uri:birthday"
m:data-type="xsd:date" m:data-value="2007-05-18">Friday next week</text:p>

Generates the following (N3-serialized) triple:

<uri:SvanteS> <uri:birthday> "2007-05-18"^^xsd:date .

In RDF/XML:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#";
         xmlns:ex="http://example.org/stuff/1.0/";>
  <rdf:Description rdf:about="uri:SvanteS">
    <ex:size
rdf:datatype="http://www.w3.org/2001/XMLSchema#date";>2007-05-18</ex:size>
  </rdf:Description>
</rdf:RDF>

Now, there's a little issue. What about the "Friday next week"? We are
losing some of that metadata.

I suggest we generate the following extra triples for the case in question:

<uri:SvanteS> <uri:birthday> [
      rdf:value "2007-05-18"^^xsd:date ;
      rdf:label "Friday next week" .
] .

Does that help clarify this?

-Elias