Simple comparison of URNs

Daniel LaLiberte (liberte@ncsa.uiuc.edu)
Sun, 25 Jun 95 23:35:36 CDT


Date: Sun, 25 Jun 95 23:35:36 CDT
From: liberte@ncsa.uiuc.edu (Daniel LaLiberte)
Message-Id: <9506260435.AA11177@void.ncsa.uiuc.edu>
To: uri@bunyip.com
Subject: Simple comparison of URNs

At the end of the path scheme draft, we included a short discussion on
the simple comparison requirement. Since the subject has come up on the
list, I'll include those paragraphs here:

The encoding requirements for URNs are met by the path scheme except
potentially for the simple comparison requirement.  The path scheme
may be used in such a way that a single resource has only one path
name, and this constraint would be consistent with the simple
comparison requirement.  But this requirement does not specify the
intended meaning of a comparison.  The intention might be that if two
URNs are compared, inequality implies that the two resources named by
the URNs must necessarily be different.  On the other hand, the
comparison might be intended only to find out if the names themselves
are supposed to be equivalent, modulo variation in character sets and
whitespace.  <p>

In general, we must allow that a single resource may have multiple
names by different naming schemes.  So the simple comparison
requirement cannot be met across multiple naming schemes.  Is there
sufficient advantage for the constraint that a resource have only one
name per naming scheme?  Tools (such as browsers and caches) should be
made to work with the knowledge that resources do not necessarily have
a single name, by perhaps remembering the canonical name for a
resource in addition to its alternative names.

---

I'd like clarification of what this simple comparison is supposed to be
used for, and then we can discuss whether it is worth it.

Daniel LaLiberte (liberte@ncsa.uiuc.edu)
National Center for Supercomputing Applications
http://union.ncsa.uiuc.edu/~liberte/