Subject: URI references and aggregation

From: [email-masked]
Date: Mon, 20 Dec 1999 12:21:13 -0800 (PST)

Over the past few months, the group has struggled with the question of
how to reference aggregations of features; we have discussed most
extensively proposals based on MD5 hashes and based on URIs.  During
those discussions, it has been clear that there were different use
cases for which different methods were more appropriate.  For very
feature and resource rich environments, URIs have some clear
advantages; for feature and resource limited environments, hashes have
advantages.  The obvious solution, support both, has been proposed
several times, but I have pushed back as chair to see if we can't come
to resolution on a single system which works across multiple 
environments.  After discussion with the document authors and IANA,
my current thought is this:

Work with IANA to change the form of the feature registry so that
registered features are directly referencable by individual URLs.  (The
current registry format is a single text page containing all of the
registered features).  This will allow us to reference registered
(unfaceted), global, and unregistered features using URLs, which has
not been possible up to this point.  

Use URLs as the pointers for feature aggregates.  As a special type of
reference, allow an object identifier URI based on the MD5 hash of the
canonical representation of the feature tag and value; the canonical
representation for the feature tags will be the URL pointer to the tag
(the value representation will continue to be set during
registration).  The MD5 hash URI could either be a unique scheme,
registered according to the recently established URI registration
guidelines, or a data URI (possibly requiring a content type
registration through the MIME processes).

I believe that this approach gives us a reasonable implementation
path for systems with a variety of resource constraints.

Please consider this carefully in light of your intended use of
the CONNEG systems, and send comments and criticism to the list.
			regards,
				Ted Hardie

---

From: "Martin J. Duerst" <[email-masked]>
Date: Tue, 21 Dec 1999 14:10:55 +0900

> not been possible up to this point.  

This is a very good step forward, not only for conneg,
but also as an example for IANA and other registries.

Regards,   Martin.

#-#-#  Martin J. Du"rst, World Wide Web Consortium
#-#-#  mailto:[email-masked]   http://www.w3.org