extraneous :'s?

I don't really understand the rationale for the :'s introduced when  
reading Qnames, and for my application (reading RDF/XML) they're an  
inconvenience.

Input file:

<rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'
	 xmlns:x="http://mumble.net/">
   <x:thing>
      <x:verb resource="http://mumble.net/thing" />
   </x:thing>
</rdf:RDF>

(call-with-input-file "loser.rdf"
        (lambda (in) (ssax:xml->sxml in '()))))
   =>
(*top* (http://www.w3.org/1999/02/22-rdf-syntax-ns#:RDF
          (http://mumble.net/:thing
            (http://mumble.net/:verb
              (@ (resource "http://mumble.net/thing"))))))

My understanding of Qnames is that the namespace prefix is  
concatenated with the name part of the Qname. The : as far as I know  
is idiosyncratic to the SXML specification. In the case of rdf/xml  
this makes a difference, since anyone processing the above rdf/xml  
will want the URI representing the x:thing Qname to be the same  
string as the value of the resource= attribute.

I can work around this by replacing Qnames with URI's that have :  
spliced out. I would need to re-insert the :'s on output.

I'm writing so that someone can explain the SXML philosophy that led  
to the :'s in the first place, so that I can tell whether this is a  
bug or a feature.

I haven't recently looked at the XML spec to see what it has dictates  
about the relations between namespaces, Qnames, and URI's - I was  
hoping someone here would save me the trouble. Is concatenation  
strictly required by XML? E.g. if you write xmlns:foo=abc and  
xmlns:bar=abcde, are the Qnames foo:defg and bar:fg *required* to be  
considered interchangeable?

Thanks
Jonathan

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