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Re: Talked to the xml.gov people

From: Paul Prescod <paul@prescod.net>
Date: Thu, 22 May 2003 19:38:32 -0700
Message-ID: <3ECD89A8.7050007@prescod.net>
To: "Bullard, Claude L (Len)" <clbullar@ingr.com>, WWW-Tag <www-tag@w3.org>

Bullard, Claude L (Len) wrote:

> Then maybe the TAG should be talking about getting rid of
> URNs altogether,

Imagine the brouhaha! Better to let them persist (heh!) not hurting 
anybody but not helping much either.

>  or explaining that HTTP really is meaningless
> to systems that provide PUBLIC to SYSTEM catalog mapping?

It isn't meaningless. It is that HTTP-based dereferencing is an 
*optional* *feature* that you can take advantage of or not depending on 
your needs.

> PUBLIC identifiers were about systems that assigned names
> but said nothing about resolution, eg, identity is assigned.
> That is the semantic.
>
> SYSTEM identifiers were about system specific locations of
> entities.  Resolving an address is the semantic.

That's true. I also came from this background and fought for PUBLIC to 
be added to XML. It took me years go conclude that I was wrong back them.

> HTTP identifiers are about names that identify locations
> of entities.  They are a SYSTEM id.  If one wants to use
> them as a name, they have two semantics.  Fine.

Fair enough. They are names that can be used as locators if that is 
convenient.

> HTTP is a protocol identifier.  Saying it is a meaningless
> string until it gets handed to an HTTP handler doen't add
> much to clarify the situation.   It just means the semantic
> to be implemented is in the handler and is fuzzy in the spec
> because the namespace specification fuzz'd it.

Not at all. The namespace specification is quite clear that when HTTP 
URIs are used in namespaces, they are used as names, not locators. The 
semantics of the specification do not depend on dereferencing. There is 
no fuzz what-so-ever. Confusion in the minds of many readers, yes. Fuzz 
in the specification, no.

> In essence, it makes no difference what goes in that namespace
> id value as long as it is unique within scope. 

That is not true. RDDL demonstrates that some namespace identifiers, 
discovered context-less in the wild, are more useful (in practice) than 
other namespace identifiers. Or to put it another way, you can do 
something with this:

SYSTEM "http://www.w3.org/2001/XMLSchema"

that you _cannot_ do with this:

PUBLIC "urn:uuid:89793274983729473298473928"

To me, that IS a difference and a significant one.

>   So why did
> Tim bother to go to xml.gov, and what of value or clarification
> did he tell them since there is no reason to prefer any string
> over another in there given a policy for mapping it to a handler,
> the semantic of which is indeterminate for the purpose of it
> being a namespace identifier?

Tim went to xml.gov to tell them that the former type of string is (in 
his and my opinion) superior to the latter because using stone age 
techniques the former can be connected to a RDDL file and a RDDL file 
can contain a wealth of important information for both a computer and a 
person.

This isn't theoretical mumbo jumbo. The URI above pointing to XML Schema 
is _really useful_. If you stumbled upon it in the wild, HTTP 
dereference would _really help you_. I don't understand under what 
circumstance it is better to cut people off from this sort of value.

  Paul Prescod
Received on Thursday, 22 May 2003 22:38:26 UTC

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