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Subject: Re: [office-metadata] RDF datatypes
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
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