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   Re: Public Identifiers

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  • From: "Steven R. Newcomb" <srn@techno.com>
  • To: xml-dev@ic.ac.uk
  • Date: Sun, 20 Sep 1998 18:57:57 -0500

Regarding FPIs (formal public identifiers) and their role (or lack
thereof) in Web applications:

(Note: in the following, I use the term "namespace" in its generic
technical sense, without reference to XML "Namespaces".  As far as I
know, this note has nothing to do with XML "Namespaces".)

Will URNs permit pointing to things that aren't now and may never be
on the web?  I mean, things that their owners never intended to be on
the web and either that their owners do not want to appear on the web,
or that their owners may not (currently) see any interest in putting
on the web?

I ask this partly because one of the interesting things in the
forthcoming Topic Navigation Map standard is the use of FPIs to point
at so-called "public topics" -- topics that are identifiable by a name
in some namespace maintained by any arbitrary authority.  All you need
is an unambiguous way to point to the authority, the namespace
maintained (or the namespace that was once created) by the authority,
and the name in that namespace.

For example, to consider a certain obsolete farm implement as a topic:

Authority: Sears, Roebuck & Co.
Namespace: 1922 Farm Catalog Number
     Name: R205

According to the current Topic Navigation Map draft (soon to be CD
13250), this would appear as the following FPI:

-//Sears, Roebuck & Co.//NONSGML TOPIC 1922 Farm Catalog Number : R205//EN

Can URNs do that?  I sure wouldn't want XML to be unable to do this
kind of thing.  If it couldn't, that would rule out the use of public
topics in XML-based topic maps.  Public topics are very useful for
correlating the knowledge contained in disparate topic maps, so the
concept of "public topics" seems pretty important to me.

You may ask, "What does non-web information have to do with the Web?"
Good question.  Personally, I think it has plenty to do with it, but I
suspect others might disagree with me.  I would venture to say that,
even today, a significant fraction of all FPIs are not intended to be
resolved, but rather simply to sit there and be pointers, documenting
the sources of authoritative material that bears on the actual online
content, but to which direct access is not needed in order for
applications to run.  One example is the FPIs of Architecture
Definition Documents in Base Architecture Declarations.  

[To HyTime aficionados, using other words, I would say that one of the
most important applications of FPIs is in lieu of biblocs.  (A HyTime
"bibloc" is a pointer to an offline resource; this facility allows
pointing to things that belong to authorities that have not endowed
them with online addresses of any kind.)]

I'm not just being provocative here; I'm really interested to hear
what the readers of this list have to say about this.  Part of the
issue is whether and how to honor the reality that people and
institutions may be regarded as authorities and keepers of
online-significant namespaces, whether or not they want to be so
regarded, and whether or not their namespaces actually exist online.
The existence of FPIs that identify namespaces that are not online
could, in sufficient numbers, and in applications of sufficient
economic importance, actually have the effect of bringing such
namespaces online.  If we take that view that the purpose of W3C
standards is to enhance human productivity by increasing the
availability of knowledge, then it's clearly desirable to have this
kind of bellwether indicator of business opportunity.  It seems to me
that we should consider the ability to reference names in offline
namespaces a requirement for XML, and so I'm glad that public
identifiers exist in XML.  Please let's not deprecate FPIs; instead,
let's understand and celebrate the difference between FPIs and URNs,
even if/when URNs are terrifically indirect.  For me, the essential
difference between URIs and FPIs has nothing to do with any particular
scheme of indirect addressing, cataloging, or algorithm for
resolution.  On the contrary, FPIs remain essential to XML precisely
because URIs, including URNs, are really system addresses, where the
system is the Web, if we consider the Web as including some array of
standardized URI resolution facilities.  FPIs are different from URIs
precisely because, for FPIs, no machine-executable resolution
algorithm is standardized, specified, or even necessarily understood,
and it's useful and vital to be able to reference things in such a


Steven R. Newcomb, President, TechnoTeacher, Inc.
srn@techno.com  http://www.techno.com  ftp.techno.com

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