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RE: URIrefs and granularity - cont.

From: Jon Hanna <jon@spin.ie>
Date: Tue, 8 Jul 2003 11:38:04 +0100
To: <www-rdf-interest@w3.org>

> For better or for worse, RDF treats URI+fragid as an opaque string. That 
> is, from the standpoint of RDF, your XPointer URI is just a URI that 
> could mean anything-- the W3C, the theory of relativity, the activity of 
> jogging in the woods, or even the union of two XML elements.

True, however other applications treat the XPointer URI as described in the XPointer specs. While the URIs used in the example are no better to RDF than any other valid URI the fact that they have semantics to other applications MAY mean they have value to a system using both such an application and RDF.

So while the use of XPointer doesn't add anything to the RDF it may add something to the RDF document. Certainly I would say that any ontology making use of XPointer should make sure such interpretations will hold.

From the first mail:
> So, in my opinion, according to the technical spec. of RDF, this statement
> is perfectly valid. However, I do have some concerns about the sematic
> meaning of it. The above-mentioned example is stating the following:
> (UNION of (http://foo/foo.xml#Item[4], http://foo/foo.xml#Item[5])) has a
> property dc:creator with value "John Doe".
> Now, one could argue if it also follows that:
> http://foo/foo.xml#Item[4] has property dc:creator with value "John Doe"
> http://foo/foo.xml#Item[5] has property dc:creator with value "John Doe"
> In a more general case, one could come up with the following example:
> Let's assume we have a subject resource-identifier pointing to an 
> XML file.
> 1. a subject: http://foo/foo.xml
> 2. a property: dc:author
> 3. an object: "John Doe"
> Then the RDF/XML syntax looks as follows:
> <?xml version="1.0"?>
> <rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#
> xmlns:dc="http://purl.org/dc/elements/1.1/">
>   <rdf:Description rdf:about=http://foo/foo.xml/>
>     <dc:author>John Doe</dc:author>
>   </rdf:Description>
> </rdf:RDF>
> The xml document that I am pointing at looks like:
> <foo>
>     <bar1>test1<bar1>
>     <bar2>test><bar2>
> </foo>
> Does this mean that John Doe is also the creator of <bar1> and <bar2>?
> According to, among others, Berners Lee
> (http://www.w3.org/DesignIssues/Identity.html), the identifier 
> refers to the
> total object described by the node, in RDF terms the 'resource'.
> Consequently, the property does also address every part of that resource.

I don't think being a sub-resource means inheriting all properties of the greater resource. Consider the predicate dc:hasPart. Clearly this can be used to describe the relationship between a resource and a sub-resource. Clearly also it is not inherited by sub-resources.

It probably is true of some resources that some properties are inherited by their parts, but in the case of dc:creator I don't think it follows. I created this email, but two parts of it were created by Jeroen Bekaert and Benja Fallenstein. The letters, punctuation and encodings all have different creators, and so on for whatever degree of reductivism you choose to pursue.
Received on Tuesday, 8 July 2003 06:35:54 GMT

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