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Re: Re[2]: XML namespaces and RDF

From: Richard Cyganiak <richard@cyganiak.de>
Date: Thu, 13 Dec 2007 23:59:17 +0000
To: Max Voelkel <voelkel@fzi.de>
Message-Id: <CA80EFDD-146E-4690-97C6-1E544FF24096@cyganiak.de>
Cc: Semantic Web <semantic-web@w3.org>, Michael Rys <mrys@microsoft.com>


On 13 Dec 2007, at 19:20, Max Voelkel wrote:
>  is    there    anywhere   a   general   rule   *defined*   how    
> to   expand
>  namespace-prefixed-XML-localnames  such  as  xs:dayTimeDuration   
> into  a  full
>  (possibly de-referencable) URI?

The prefix:localname syntax is used all over the RDF world, but  
nevertheless it is *not* part of the core RDF standard. There's no  
single place where it is defined. The RDF abstract model doesn't know  
about this abbreviation mechanism at all; it just knows about fullly  
expanded, absolute URIs.

The prefix:localname syntax is just a convention that is used in  
multiple RDF serialization formats and other RDF-related standards, to  
the point where it has become ubiquitous. Hence you have to consult  
the specs for the individual formats that use this syntax.

For RDF/XML, try this:

"Within RDF/XML, XML QNames are transformed into RDF URI references by  
appending the XML local name to the namespace name (URI reference).  
For example, if the XML namespace prefix foo has namespace name (URI  
reference)http://example.org/somewhere/ then the QName foo:bar would  
correspond to the RDF URI referencehttp://example.org/somewhere/bar.  
Note that this restricts which RDF URI references can be made and the  
same URI can be given in multiple ways."

For Turtle, try section 2.1:

"Once a prefix such as @prefix foo: <http://example.org/ns#> is  
defined, any mention of a URI later in the document may use a  
qualified name that starts foo: to stand for the longer URI. So for  
example, the qualified name foo:bar is a shorthand for the URI http://example.org/ns#bar 

SPARQL also has it:

"The PREFIX keyword associates a prefix label with an IRI. A prefixed  
name is a prefix label and a local part, separated by a colon ":". A  
prefixed name is mapped to an IRI by concatenating the IRI associated  
with the prefix and the local part. The prefix label or the local part  
may be empty. Note that SPARQL local names allow leading digits while  
XML local names do not."

I'm sure there are more.


> ----------
> in http://www.w3.org/TR/xpath-datamodel/#notation it says:
> ----
> The following bindings are assumed.
> xs: bound to http://www.w3.org/2001/XMLSchema
> ----
> This implies from XML namespace rules that e.g.
> xs:dayTimeDuration  expands to
> http://www.w3.org/2001/XMLSchemadayTimeDuration
> which is not a dereferencable URI.
> Is   this correct and intended? For RDF, one uses usually namespace  
> declarations
> that end with "/" or "#".
> Michael Rys responds:
> MR> Namespace prefixes in XML are not concatenated to the names in  
> the way that
> MR> you do it below. Instead they form a tuple
> MR> (namespace-uri, local-name).
> MR> There are different expanded name notations being used, such as
> MR> {http://www.w3.org/2001/XMLSchema}dayTimeDuration,
> MR> which is non-dereferencable, or
> MR> http://www.w3.org/2001/XMLSchema#dayTimeDuration which can be.
> Thanks  a  lot for your quick response. Is there a sort of  
> authorative "expanded
> name   notation"?   Especially  one  talking  about  "#"  would    
> be  great  to
> read/reference. I have no idea what to Google for.
> [1] 'defines' (but only in the examples) the rule: <url> =   
> <namespace> + <localname>
> [1] http://www.w3.org/TR/rdf-primer/
> Kind Regards,
> Max
> --
>       Max Völkel
>       voelkel@fzi.de | www.Xam.de
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>       mobile     +49 171 83 59 678
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Received on Thursday, 13 December 2007 23:59:27 UTC

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