[urn] URNs are not URIs (another look at RFC 3986)

[John C Klensin <[e-mail]>]

Hi.

It seems wise to call the attention of this broader group to
something that is going on in URNBIS (and more generally).
This message is a personal opinion.  It summarizes some
discussions in and around that WG but is not an attempt to
report on any sort of consensus.

RFC 3986 on Generic URI Syntax was an attempt to create a
general syntax (and, despite its title, partial semantics) for
an extremely general set of resource identifiers, using
experience with and developments from URLs as a starting point.
The general URI concept was intended to including URLs, URNs,
and possible future types.  That approach worked for URNs as
long as they preserved the very narrow definitions and syntax of
RFC 2141 but without taking advantage of any of the provisions
for extensibility ("future use") in that specification.

In the nearly 20 years since RFC 2141 was published, experience
with URNs in various communities has demonstrated the need, with
some URN types (NIDs), to be able to specify operations or
retrieval of metadata as well as objects and for partial
retrieval or other operations on either metadata of the objects
themselves.  At the same time, there have been forceful
discussions in information science, library, museum, and
publisher communities about the fundamental differences between
locators and names (which much of that community calls
"identifiers", excluding locators from that category) and the
disadvantages of mixing the two concepts.  That might be mostly
a theoretical issue except that the URNBIS WG has found it
impossible to define the functionality it needs while remaining
within the syntax and semantic constraints of RFC 3986 (at least
without creating obvious and very ugly kludges).  

The WG is now considering
draft-ietf-urnbis-urns-are-not-uris-00, which proposes to
separate URNs from RFC 3986, presumably leaving the latter with
URLs and name-like things that are not URNs.   It may be worth
noting that there is now work in W3C and WHATWG on a new URL
definition.  The intent of that work includes eventually
superceding 3986 (and 3987), at least for URLs, so there are
multiple forces working to dismember RFC 3986.  However, the
URNBIS draft is intended to narrowly focus on the needs of URNs,
rather than trying to boil the URI ocean.

Those who are interested in this topic should probably take a
look at the draft and the discussions during the last week or so
on the URN mailing list
(http://www.ietf.org/mail-archive/web/urn/).   That list has
been fairly low-volume, so looking at those messages should not
be burdensome.  Discussion should also occur on that list unless
there are very broad issues that belong here.

thanks,
   john