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Re: URIs for terms: motivation [was: Requirements Document]

From: Dan Connolly <connolly@w3.org>
Date: 08 Feb 2002 16:57:53 -0600
To: "Peter F. "Patel-Schneider <pfps@research.bell-labs.com>
Cc: www-webont-wg@w3.org
Message-Id: <1013209074.1708.62.camel@dirk>
On Fri, 2002-02-08 at 16:01, Peter F. Patel-Schneider wrote:
> Your message is an excellent condensation of some of the most-important
> aspects of the WWW.  
> 
> Thanks.

Welcome.

> Now on to technical points:
> 
> 1/ I believe that you actually don't want URIs in the requirement, but URIs
>    plus fragment indentifiers.

Well, in terms of what I want, I want a new URI spec that makes
it clear that fragments are part of URIs, like they were
in the first place. cf RFC1630, June 1994; or even earlier...
http://www.w3.org/History/19921103-hypertext/hypertext/WWW/Addressing/BNF.html#47

But in terms of what's practical in the timeframe we intend
to publish this document, yes, "absolute URI reference"
is probably the right term.

> 2/ I believe that you actually don't want QNames to be syntactic shorthand
>    for URIs, but instead want them to be syntactic shorthand for URIs plus
>    fragment identifiers,

Yes...

> and, moreover, that the local part of the QName
>    corresponds to the fragment identifier.

Um... I haven't made up my mind on that, personally. But
I represent folks who do, yes.


> 3/ I want to have some mechanism in OWL that can be used to identify
>    (global?) XML Schema declarations.

Do you mean schema components or declarations?

(cf http://www.w3.org/TR/xmlschema-1/#intro-terminology)

I want to be able to refer to XML Schema components
(or types or something) too...

>  XML Schema seems to indicate that
>    URIs plus fragment identifiers cannot be used for this purpose,

Actually, it doesn't say that they cannot; it just doesn't
make it quite clear that they can, nor how.

As I pointed out, they don't consider this a long-term solution.
More recent work is starting to address this issue:

  "2.1  Normalization

  We use a normalized form of a schema, which assigns a
  unique universal name to each component of a schema"
  --
http://www.w3.org/TR/2001/WD-xmlschema-formal-20010925/#section-overview-normalization

also:

  "Status of this document
  Parts of this specification, such as the normalization of names,
  may eventually find a broader use."
  -- http://www.w3.org/TR/xmlschema-formal/

> so I want
>    something more than URIs plus fragment identifiers.  

I want to be sure URIs(+fragids) can refer to XML Schema components.
I should tell the www-xml-schema-comments; I think they're
collecting 1.1 requirements now, after all.


> Why don't URIs plus fragment identifiers work for XML Schema?  Well, I
> guess that it is because there can be several portions of an XML Schema
> with the same ``name''.  That is, there can be both a global type
> definition and a global element declaration with the same name in an XML
> Schema document, and both of these are referred to by the same QName.
> 
> Is this a bug?  Maybe.  Is it motivated by compatability-with-DTD reasons?
> I don't think so.  Will it go away?  I don't know, but I'm sure that there
> would be howls if elements and attributes had to have different names.
> 
> What can we do?  I really don't know. All I know is that I want to be able
> to incorporate XML Schema definitions into ontologies, maybe not now, but
> certainly later.

On that we seem to agree; perhaps it's worth adding something to
that effect in the requiremens document? Hmm...


> It does occur to me that there are ways around the problem.  For example, I
> don't see a reason that forbids the splitting of the XML Schema URI plus
> fragment namespace into different sub-spaces.  To refer to a global element
> definition, you would use foo:element.bar and foo:attribute.bar for a
> global attribute definition.  This would result in different URIs plus
> fragments for the different definitions.  In XML you could still use
> foo:bar as an element name and foo:bar as an attribute name.

That's the sort of thing I think they're looking at.

>  Would this
> cause howls of outrage?  I'm not sure.

I haven't heard of any. Taking a look at the archive of comments...

http://lists.w3.org/Archives/Public/www-xml-schema-comments/2002JanMar/thread.html

sigh. tons of spam. Hard to say if there have been any complaints.


I don't suppose I've convinced you that we should stick to the
"use URIs(+fragids) for terms" requirement, have I?


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Friday, 8 February 2002 17:57:43 GMT

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