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   RE: URN Madness (was re: Overloaded URIs must GO!)

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  • From: "Didier PH Martin" <martind@netfolder.com>
  • To: "'XML Dev'" <xml-dev@ic.ac.uk>
  • Date: Fri, 28 May 1999 19:54:04 -0400

Hi David,

David said:
That's what I meant by "the URN schemes are not yet defined" (or
whatever my wording was).  In other words, URNs are not yet safe to
use for XML Namespace URIs outside of the IETF (x-* URN namespaces are
not guaranteed unique), but they may be soon.  For now, we have to
keep using URLs.

Didier says:
Here is the simple mechanism the W3C can do (And the sentence "outside of
IETF" has no real meaning unless you mean that outside W3c there is nothing

Scenario: URN is used to obtain a document.
a) W3C reserve a namespace and send to IANA a URN registration paper.
b) install a DNS server and enter the right records to resolve URNs into
URLs (for each "official schemas")
c) All parsers in need to get a document about a particular name space (like
for instance a schema or a DTD) could then use the DNS protocol (and of
course connect to the W3C server - or the backup server)
d) Then, all the URNs would be resolved as URLs and the document downloaded
with the right protocol

So, there is maybe something I am missing. Why is URNs not safe for XML name

If we use URLs is it simply to fill an empty space :-) or is it because it
points to a place where a document is stored? If it is because it points to
a location where a document is stored. A URL has the disadvantage that if
you change the location of this document, all documents having a reference
to this location are no pointing to the right location and could not
practically be validated.
Do we sell XML as having a longer shelf life than other formats? If yes,
URLs are dangerous because they are tightly connected to the location (the
name itself tells it all a U_niversal R_esource **L_ocation**). A URN gives
you location independence, the document may be moved to a different place
and the URN will be still valid. You'll just have to change the DNS record
but won't have to change every single document in the field.

Have you read carefully not the drafts _but_ the **RFC 2141**. If yes, after
this reading, what is the problem you have with URNs and what is your
argument about the location problem inherent to URLs. What if we move the
document form one location -URL- to a new one?

Note: The official name space documentation may not necessarily be W3 but a
registry somewhere so that people could register their official name space
documentation (i.e for example a schema or DTD).You'll also resolve other
problems with such registry like for instance e-commerce.

Didier PH Martin

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