RE: RDF and xml:base

Graham Klyne [mailto:GK@ninebynine.org] wrote:

>At 11:19 AM 5/29/01 +0100, Lee Jonas wrote:
>
>
>>Graham Klyne [mailto:GK@ninebynine.org] wrote:
>>
>>[snip]
>> >Under these circumstances, there is some confusion about the meaning and
>> >usability of rdf:ID= to identify an RDF resource.  I think the confusion
>> >can be resolved if an xml:base attribute is used to create a base URI
for
>> >such cases.  It may be necessary to check the definition of rdf:ID to be
>> >sure that xml:base applies.
>>[snip]
>>
>>I took rdf:ID to have the equivalent semantics as an XML attribute of type
>>'ID'.  If this is the case, then xml:base won't affect the absolute
>>URI-reference for the RDFresource defined - AFAIK, '#fragid' is always a
>>fragment within the current document, regardless of the base URI.
>
>But what is it to mean in the corresponding RDF graph ("model"), which may 
>exist without reference to the containing document?
>
>#g
>

Following on from your earlier example of a transient protocol stream:

Arguably, a locally defined RDFResource (with an rdf:ID attribute) is a
fragment of the transient RDF stream.  You don't need an absolute
URI-reference to refer to it whilst processing the stream, just the
fragment.  Once processing is finished its transient nature means that
persistent references to it are meaningless.  I.e. no document URI => no
absolute URI-reference for a locally defined RDFResource.

If the stream is merely a transport for some persistent RDF document and you
want to keep its persistent nature intact, you could do one of the
following:
1) specify some protocol-specific way to communicate the source document's
URI and process accordingly.
2) translate all 'rdf:ID's to 'rdf:about's (i.e. absolute URI-references)
using the source document's URI before transmission.
etc.

The key point is that none of this has anything to do with xml:base.  XML
Base is used to set base URIs for relative URI resolution:

From the URI resolution algorithm in rfc2396:

"2) If the path component is empty and the scheme, authority, and
    query components are undefined, then it is a reference to the
    current document and we are done."

i.e. a fragment on its own is a reference to the current document.  The
following comes into play iff the URI-reference is not absolute yet contains
more than just a fragment:

"6) If this step is reached, then we are resolving a relative-path
    reference.  The relative path needs to be merged with the base
    URI's path."

I.e. it is a well defined process that cannot indicate/override a document
URI given a fragment only.

regards

Lee



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Received on Tuesday, 29 May 2001 10:55:28 UTC