Re: URIs quack like a duck

John Cowan wrote:

> > The other contexts [neither namespace spec nor XPath] involve retrieval, not
> comparison.
>
> Not necessarily!  RDF does not require retrieval; it requires
> RFC 2396 comparison.  In other words, you use RDF to say
> something *about* a resource which can be identified (not
> necessarily retrieved) by a URI.  The URI doesn't even have
> to refer to a resource that *can* be received, as in these
> examples:
>
>         <rdf:Description about="brick:us/ny/nyc/13%20E.%203rd%20St?course=3;serial=20">
>                 <xx:color>red</xx:color>
>         </rdf:Description>
>
>         <rdf:Description about="mailto:cowan@ccil.org">
>                 <yy:cost>free</yy:cost>
>         </rdf:Description>
>
> These say that a certain brick is red and that a certain mailbox is
> free of charge.  In neither case does it make sense to try to access
> the URI.

Sorry, I wasn't clear.  I was talking about comparing URI1 with URI2.  Does RDF ever do
that?

I understand that RDF can say something about a resource that can be identified but not
necessarily retrieved.   Perhaps if I had said "retrieval or identification" instead of
"retrieval", that would have been better, and the point would remain true.  The essential
observation is that comparison of one URI with another URI is not involved.

When you refer to RFC2396 comparison, are you talking about comparing one URI with another
or about something else?  I don't see anything in RFC2396 that talks about comparing one
URI with another, but perhaps I just missed it.

> > If we treat "data:," as a benediction that we place on URIs
> > to make them kosher for
> > use as namespace names and discourage the use of all others,
>
> What I am recommending is leaving namespace *names* alone, and
> prefixing them with "data:," when we need to create *URIs* for
> namespaces.

Let's see if I understand it now.  A namespace is a resource, so we want to have some way
of using aURI to refer to it.  The "data:," provides such a way.    So if we have

     ... xmlns:foo="http://www.sushi.edu/octopi" ...

then "data:,http://www.sushi.edu/octopi" provides a way to refer to that namespace in
other contexts.  Right?

Paul Abrahams

Received on Friday, 2 June 2000 23:20:45 UTC