W3C home > Mailing lists > Public > www-rdf-interest@w3.org > June 2001

Re: URI etymology

From: Jonathan Borden <jborden@mediaone.net>
Date: Mon, 11 Jun 2001 12:05:22 -0400
Message-ID: <006a01c0f290$5205fb30$0a2e249b@nemc.org>
To: "Pierre-Antoine CHAMPIN" <champin@bat710.univ-lyon1.fr>
Cc: <www-rdf-interest@w3.org>
Pierre-Antoine CHAMPIN wrote:

> On 11 Jun 2001 06:31:52 -0400, Jonathan Borden wrote:
> > Certainly an "http:" URI can identify a namespace, most namespace names
> > common usage are http: prefixed.
> > (...)
> > XML and XML applications see no "semantic ambiguity". The only ambiguity
> > see is that which is attached by humans trying to read the tea leaves.
> This is only true because such URIs are used in a very precise contex:
> xmlns* attributes.
> Any string used in those attributes is supposed to identify nothing but
> a namespace, so there is no ambiguity indeed !

Where is this "supposed to identify nothing but ..." language from. As I
said, an XML namespace is for use by software as it sees fit. Beyong the
directives in the XML Namespaces recommendation, basically:

1) an XML namespace name is a URI reference
2) XML namespace names are to be compared by literal string comparison
3) XML namespace prefixes are bound to a namespace URI according to the
provided scoping rules.
4) unprefixed child elements inherit the default namespace of their parent
5) unprefixed attributes do not inherit the namespace of their containing

the XML namespaces recommendation attaches no semantics to a namespace name
or URI.

> What I think is that URIs are not opaque names,
> although http://www.w3.org/DesignIssues/Axioms.html reads
>   Axiom: Opacity of URIs
>   The only thing you can use an identifier for is to refer to an object.
> When you are not dereferencing you   should not look at the contents of
> the URI string to gain other information.
> How would I know which URIs I may try to dereference, anyway, without
> looking "inside" it ?
> URIs have a rather precise syntax described in RDF2396. That syntax may
> be used not only to know how to dereference a URI, but also *if* I may
> dereference it, and what kind of resource it identifies.

you are missing the point. assume that "trying to figure out how to
dereference a URI" is part of the dereferencing process, e.g. Microsoft IE.x
is free to attach a piece of code that dereferences "urn:" scheme URIs.
_Nothing prohibits this_

> If I'm wrong, what are the advantages of the Opacity axiom ?

    How about ... just below... i.e. that any URI can be used as a namespace
name if one so chooses.

> If I'm right, then any URI can bnot be use to identify any resource...
> including namespaces.

    What you seem to be asking for _could_ be accomplished by
rdf:aboutEachPrefix. e.g. rdf:aboutEachPrefix="http:" ... constraints go
here ...

Received on Monday, 11 June 2001 12:22:27 UTC

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