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   re URN, URL, URI

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  • From: Terry Allen <tallen@sonic.net>
  • To: xml-dev@ic.ac.uk
  • Date: Thu, 22 Oct 1998 06:55:48 -0700

Amit Rekhi wrote:
| Hello,
|             After having gone through the URI specs at the w3c site I wanted
| to confirm a few doubts. I'd be grateful if anyone would kindly help.

Assuming these are the current versions of the specifications from the
IETF, where the URN work is done:

| DOUBT 1 :- URNs at this point are not widely used since there is no
| generally available resolution service. In case a resolution infrastructure
| comes up in time :-

There is a generally available resolution mechanism, through DNS, but
it has not implemented except on a test basis so far as I know.  URNs,
of course, may be useful within more constrained contexts.  Note that 
URN resolution won't happen for you without some effort on your part.

| * Where would the service reside(client/server)?

You would want to have resolution hints on the client end, and be
able to check your cache for documents you already have; otherwise
consult RFC 2168 for the DNS approach.

| * Would the server simply serve all the docs that contain FPIs to the client
| or would it resolve the FPIs to system IDs before serving the docs to the
| client or would it "selectively" serve files depending upon the FPIs it can
| resolve?

A URN resolution service will only resolve URNs.  It might be coupled with
a document server, but that's another matter.  RFC 2168 indicates the
possible services that could be specified (N2N, N2L), but there is no
requirement that a resolution services support any particular one of
them, I believe.

An FPI as it stands is not a URN, but were an FPI name space defined
for URN use, FPIs can be escaped and encoded as URNs.

| * Would the client in anyway be involved in resolving the FPI -> Sys ID?

If the URN resolution service returns a URL, presumably you'd want the
client to resolve the URL.

| DOUBT 2 :- URN simply stated refers to a globally unique, persistent  name
| from a NameSpace. This name could be used to provide a  label to resources.
| * Could a URN also label a resource which may not necessarily be residing on
| the web?
| ( I could label a resource with a URN ,and the resource could very well be a
| set of paper documents!
| This could happen in a scenario where 2 parties provide a paper resource
| with a URN and transmit only the URN in their XML files to each other. The
| resource could be transmitted  on paper since it is a set of paper
| documents )

Yes.  This is not a bug.

| DOUBT 3 :- Talking in terms of URI, if a URI is not a URLthen it HAS to be a
| URN and vice versa. Am I right?

At this point, yes.  URCs were talked about, but those interested in URCs
are now mostly doing RDF.

regards, Terry Allen

Terry Allen				Veo Systems, Inc.
Business Language Designer	        2440 W. El Camino Real
tallen[at]sonic.net                     Mountain View, Calif., 94040
Common Business Library - available at  http://www.veosystems.com/

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