xml-dev - Re: Just require URLs

["Jonathan Borden" <jborden@mediaone.net>]

Paul Prescod wrote:

>Jonathan Borden wrote:
>>
>
>> Note that when the string "http://www.w3.org/xxx" is used as an XML
>> namespace URI this is a URN not a URL by definition (the scheme remains
>> "http").
>
>That string is not syntactically a URN. Please see RFC 2141. It is quite
>explicit:
>
>All URNs have the following syntax (phrases enclosed in quotes are
>REQUIRED):
>
>                     <URN> ::= "urn:" <NID> ":" <NSS>
>
>If I'm right on this issue (and what room is there for dispute) and you
>are right that it cannot be interpreted as a URL in the context that we
>are discussing (more subtle but still, I think right) then you must agree
>with me that this is not a URI *of any sort* and thus in violation of the
>namespaces specification which is both clear and consistent in this
>regard.
>

    My reading of RFC 2396 suggests that the intention is to supercede the
definitions of both URLs and URNs. Interestingly 2396 defines 'resource' as
either an abstract or physical entity, an example of an abstract entity
would be a namespace. A physical resource would be a document. What is not
explicitly specified is whether the same URI may 'point' or name 2 separate
resources, 1) an abstract resource e.g. namespace, property etc, and at the
same time 2) a physical resource e.g. schema document. Clearly however, when
used in XML namespaces and if the namespace URI *does* point to a schema
document (this is outside the namespace spec) the URI does denote 2 distinct
resources.

    Under the definition of URN in 2396, a URN is any URI whose intention is
to reference an abstract resource, act primarily as a name, and/or not be
retrievable via a network. Under the definition in 2396, "urn" defines a
scheme/namespace (URI namespace) whose intention is to serve *only* for
URNs, however the spec suggests that any scheme e.g. "http" can serve to
define a URN, given the definition of URN in 2396 (part of which my earlier
message quotes).

    So, my reading of RFC 2396 and the XML namespace spec leads me to
conclude that all URIs used as XML namespaces are properly URNs regardless
of the URI scheme prefix.

Jonathan Borden
http://jabr.ne.mediaone.net



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