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Re: [ALL] xml:base and URIs with hashes

From: Graham Klyne <GK@ninebynine.org>
Date: Mon, 23 Jan 2006 10:26:40 +0000
Message-ID: <43D4AF60.6060309@ninebynine.org>
To: "Miles, AJ \(Alistair\)" <A.J.Miles@rl.ac.uk>
CC: public-swbp-wg@w3.org, semantic-web@w3.org

According to RFC 3986 [1], a base URI is not permitted to have a fragment.  See
sections 5.1 and 4.3.

#g
--

[1] http://www.ietf.org/rfc/rfc3986.txt


Miles, AJ (Alistair) wrote:
> Just putting this on the record ...
> 
> I've just discovered a technical detail wrt xml:base attribute in RDF/XML docs - if you put a hash at the end of the base URI it is ignored when constructing relative URIs.
> 
> I.e. the following RDF/XML:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <rdf:RDF 
>   xml:base="http://example.com/foo#"
>   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>   xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
>   
>   <rdf:Description rdf:about="">
>     <rdfs:label>this</rdfs:label>
>   </rdf:Description>
>  
> </rdf:RDF>
> 
> ... gives the following triple:
> 
> <http://example.com/foo> rdfs:label "this".
> 
> It doesn't matter if you put more than one hash at the end of the base URI, they are all ignored. I.e. the following RDF/XML:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <rdf:RDF 
>   xml:base="http://example.com/foo####"
>   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>   xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
>   
>   <rdf:Description rdf:about="">
>     <rdfs:label>this</rdfs:label>
>   </rdf:Description>
>  
> </rdf:RDF>
> 	
> ... gives the same triple as above:
> 
> <http://example.com/foo> rdfs:label "this".
> 
> Note however that the absolute URI <http://example.com/spong> is treated by RDF parsers as different from the absolute URI <http://example.com/spong#> (which spec can verify that this?).  I.e. the following RDF/XML:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <rdf:RDF 
>   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>   xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
> 
>   <rdf:Description rdf:about="http://example.com/spong#">
>     <rdfs:label>spong#</rdfs:label>
>   </rdf:Description>
>     
>   <rdf:Description rdf:about="http://example.com/spong">
>     <rdfs:label>spong</rdfs:label>
>   </rdf:Description>
> 
> </rdf:RDF>
> 
> ... gives the following triples:
> 
> <http://example.com/spong#> rdfs:label "spong#".
> <http://example.com/spong> rdfs:label "spong".
> 
> Interestingly, the URI <http://example.com/spong##> raises an error when using the W3C RDF validation service (running ARP) - 
> 
> Error: {W107} Bad URI <http://elsewhere.org/spong##>: Fragment contains invalid character:#
> 
> However, Sesame 1.2.3 doesn't raise an error, and creates a new URI resource in the graph.
> 
> I remember vaguely Jeremy Carroll saying that hashes are actually allowed in fragment ids ... is this right or wrong?
> 
> Finally, this has implications for RDFS/OWL vocabularies/ontologies that use a hash namespace, because it means we have to be careful not to confuse the 'vocabulary URI' (a.k.a. the 'ontology URI', i.e. the URI that identifies the vocabulary/ontology) and the 'namespace URI' (i.e. the actual URI you append the local name of each term to). E.g. 
> 
> http://example.com/vocab - vocabulary URI.
> http://example.com/vocab# - namespace URI. 
> 
> For RDFS/OWL vocabularies/ontologies that use a slash namespace both the vocabulary URI and the namespace URI are the same, e.g.
> 
> http://example.com/anothervocab/ - vocabulary URI.
> http://example.com/anothervocab/ - namespace URI.
> 
> Cheers,
> 
> Al.
> 
> ---
> Alistair Miles
> Research Associate
> CCLRC - Rutherford Appleton Laboratory
> Building R1 Room 1.60
> Fermi Avenue
> Chilton
> Didcot
> Oxfordshire OX11 0QX
> United Kingdom
> Email:        a.j.miles@rl.ac.uk
> Tel: +44 (0)1235 445440
> 
> 
> 

-- 
Graham Klyne
For email:
http://www.ninebynine.org/#Contact
Received on Monday, 23 January 2006 10:31:32 GMT

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