Stab at URNs in the dark

Terry Allen (
Fri, 18 Mar 1994 23:09:00 --100

| Return-Path: <>
| Date: Fri, 18 Mar 1994 20:49:16 --100
| Message-Id: <>
| From: "Daniel W. Connolly" <>
| Subject: Reliable links [Was: Stab in the dark ]
| . . . Larry Masinter writes:
| >
| >If URNs are allowed to refer to multiple formats of documents, or
| >multiple versions of updating documents, or online streams of
| >information that you might telnet to, then ...
| .. then you can't do anything reliably!!!! Ha Ha Ha!!! I've been
| trying to make this point for TWO YEARS!

We need something to do exactly these things, though. If not
URNs then what, Dan? (you write of URIs later on)

| There is some value in having names for things that are not defined
| as octet streams (fulltext indexes, newsgroups, FTP directories, etc.)
| but as it is, we are missing out on the tremendous value of taking
| advantage of the multitude of things that _are_ defined as octet
| streams: software distributions, documents (once represented in some
| format), news articles, email messages, ... ... ...

These are the trivial cases: no versions, no variety of languages,
no variety of formats. Solve the harder cases and the solution to
these falls out.

| But in either case, you can give the same url twice and there's no
| mechanism to guarantee that you'll get the same thing back, and no way
| to test to see if you did!

Sure there is. Save it the first time, or save its digital signature.
If digital signatures of documents were disseminated publicly
at the time of publication, one could even authenticate a doc
from an untrusted, even untrustworthy source. Only some such
mechanism will replace the binding of reference with target you
mention below:

| Isn't this the basic feature of a
| reference, link, or citation? I write "See page 123 for info on
| Widget Co." with the understanding that when my reader turns to page
| 123, he'll see the same information I'm talking about.
| With paper book publishing, the reference is bound with the target
| information at publishing time. But in a distributed system, different
| parts of the information base are changing at different times.

That is the case when documents are being revised continuously *and*
previous recensions are not being archived. But I can also have
the same info available in a variety of renderings, all using
the same reference scheme (the page numbers of a reference
format, if desired). Now what am I going to use to call that collection,
or the archive of all versions of a doc throughout time, if I bother
to save them all? and what information does the URN > URL resolver
need to distinguish among versions, formats, and other possible
variations *of the same literary work*? (Sameness being determined initially
by the publisher and maybe revised a bit by librarians and archivists.)

If you supply a URN that doesn't point to a unique thing, then
you'll either get a list of URLs back or you'll have to supply
extra info alongside the URN (for the URN designating the Los
Angeles Times, give me the latest city edition, sports section).

Terry Allen  (
Editor, Digital Media Group
O'Reilly & Associates, Inc.
Sebastopol, Calif., 95472