Public Identifiers

John Cowan cowan at
Wed Sep 23 20:06:03 BST 1998

W. Eliot Kimber scripsit:

> [T]he PUBLIC/SYSTEM distinction made by
> SGML (and XML) is inappropriate as a matter of syntax.  A name is a name
> and there should be exactly one declared for each entity.

However, there is a difference between a name (FPI or URN) and
an address (URL), which does not quite correlate with PUBLIC
vs. SYSTEM.  IMHO this distinction is very much worth maintaining.

When we address postal mail, we generally
supply both a name and an address, and the postal system primarily
uses the address to deliver mail.  (There may be indirection within the
address system, as when mail is forwarded, or through P.O. boxes, but that's
another matter.)  If address-based delivery fails, the postal
tries to use name-based delivery (I have gotten mail addressed
to "John Cowan" at all sorts of random addresses in my city).

Resulting maxims:

	1) My name is not simply an indirect way of indicating
	my address!

	2) Names tell us "who", addresses tell us "where".

> URN resolution mechanisms should be independent of the syntax used for the
> binding--they should simply expect two arguments, a name-space name and a
> name in that name space. How the client that makes the resolution request
> gets those two arguments is its business.

Having a single syntax makes the interface between a client stub and
a general resolver (as opposed to namespace-specific resolvers)

> Given that my analysis is correct, here's what I'd like to see happen:
> 1. A general recognition of the need for name-space/name bindings in data
> representation standards, regardless of the kind of data.  If these
> bindings are further standardized along the URN lines (its semantics, not
> its syntax, necessarily), so much the better.


> 2. Given item (1), data management systems (including operating systems and
> networking systems) providing generalized name-space-to-resolver services
> that reflect the general approach defined by item (1).  For Internet-based
> resources, the DNS proposal is probably appropriate and reasonable.

> 3. Web clients upgraded to accept "urn:url:" as a prefix to otherwise
> normal URLs.

I disagree, as that would blur an essential distinction.
> 4. People and enterprises providing non-URL name resolution servers.  These
> could be along the lines of the PURL services currently being provided (and
> could probably be implemented with the existing PURL software).  For
> example, Oasis could fund a couple of public identifier servers.

Three cheers!

> And now, having said that SGML formal public identifiers have no special
> properties, let me point out that the fact that registered formal public
> identifiers are registered means that you could use owner names to direct
> public ID resolution to servers maintained by the name owner, rather than
> relying on a central FPI resolution server (that is, "DNS for FPIs").

DELEGATE was born to make this work.

> If I
> understand the DNS-for-URN resolution proposal (which I very well may not,
> not being an Internet expert by any stretch), the ability to do this is
> inherent in the proposal.

The maxim here is: If you need a distributed database on the Internet,
try to use the DNS if you can, because it is robust, scaleable,
and --- most importantly --- already there.

John Cowan		cowan at
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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