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RE: [rdfmsQnameUriMapping-6] CLOSED: Algorithm for creating a URI from a QName?

From: Williams, Stuart <skw@hp.com>
Date: Wed, 3 Dec 2003 14:24:44 -0000
Message-ID: <E864E95CB35C1C46B72FEA0626A2E80869A3BE@0-mail-br1.hpl.hp.com>
To: "'ht@cogsci.ed.ac.uk'" <ht@cogsci.ed.ac.uk>, "Ian B. Jacobs" <ij@w3.org>
Cc: jborden@mediaone.net, www-tag@w3.org

Henry, Ian,

I think there may be made a mistake in referring to "Using Qualified Names
(QNames) as Identifiers in Content" [1] in reporting the closure of issue 6
[2]. 

That finding explicitly states [3]:

     "A related TAG issue, rdfmsQnameUriMapping-6, concerns the 
      mechanism by which one can (or can not) construct a URI 
     for a particular QName. We do not consider that issue in 
     this finding."

which would place it outside the scope of issue 6.

The prinicple in the finding is focused on the mapping of qnames (ie
prefix:local) to qualified names (ie {URI, localname} tuples). 

The "Good Practice Note" in the architecture document, currently stated as

	"Good practice: QName Mapping: Language designers who use QNames
MUST provide a mapping to URIs."

has a different focus. It is focussed on mapping between Qnames and URI.
This was discussed at the November TAG F2F [4] (and log extract below). It
is intended to cover cases where language designers are using qnames as way
of convey URI/URI reference. Where I thought we landed was at the statement
Ian quoted [4] from our minutes:

  "The use of Qnames as identifiers without providing a mapping to 
   URIs is inconsistent with Web Architecture." 

   (omitting the reference to the qnameId finding)

The "as identifiers" qualification has not (yet) propagated into the
architecture document. I don't know if that qualification would address
Henry's concern. I might be tempted to tighten the GPN language further to
say: 

	"Good practice: QName Mapping: Language designers who use Qnames as
a means to convey URI MUST provide a mapping to URIs."

I don't believe a mapping to URI is necessary when a qname is being used to
convey a qualified name! 

I believe that the TAGs intent is that where qnames are used as a means of
identifying a Web Resource then there is a burden of the language designer
to provide an explicit mapping between qnames used in the context of that
language and URI that identify the same resource.

Regards

Stuart
--
[1] http://www.w3.org/2001/tag/doc/qnameids.html
[2] http://www.w3.org/mid/1070385456.16926.79.camel@seabright
[3] http://www.w3.org/2001/tag/doc/qnameids.html#sec-qnamesids
[4] http://www.w3.org/2003/11/15-tag-summary.html#formats

<logExtract>
4.6.2. Links and Qnames in XML 
DO: We need to say more about the badness of QNames. For example, Give an
example of qnames harmful. Canonicalization: you can lose the target
namespace. 
TB: I agree with DO. 
DO: "Format specification authors who use QNames MUST provide a mapping to
URIs". This should be SHOULD. 
TB, NW, CL: No, MUST. 
SW: Two nuances: 
    1. Is there a mapping from qnames to URIs? 
    2. Is a qualified name something other than a URI? 
SW: If someone is using a Qname because that meets their needs, why should
we obligate them to use a URI? 
DC: They are using things other than URIs to refer to things; that's a
no-no. URI Refs are not URIs; they are mapped to URIs. 
TB: Recast this as follows: "The use of Qnames as identifiers without
providing a mapping to URIs is inconsistent with Web Architecture" 
CL noting on 4.6.1: "The data's usefulness should outlive the tools
currently used to process it." Please don't imply that can't use XML for
short-lived things. 
DC: I like TB's proposal somewhat; I think that this closes issue 6. 
    - Use URIs as identifiers 
    - If you use Qnames, provide a mapping to URIs. 
    - The use of Qnames as identifiers without providing a mapping to URIs
is inconsistent with Web Architecture" 
Cite RDF and Schemanons, abscomponentrefs (existing mappings) 
Resolved: Close issue 6 with TB language: "The use of Qnames as identifiers
without providing a mapping to URIs is inconsistent with Web Architecture". 
Action IJ: 
Close issue 
Send email to person who raised issue.
</logExtract>

> -----Original Message-----
> From: ht@cogsci.ed.ac.uk [mailto:ht@cogsci.ed.ac.uk] 
> Sent: 3 December 2003 10:26
> To: Ian B. Jacobs
> Cc: jborden@mediaone.net; www-tag@w3.org
> Subject: Re: [rdfmsQnameUriMapping-6] CLOSED: Algorithm for 
> creating a URI from a QName?
> 
> 
> 
> I'm concerned that there's a significant different between 
> the words in the finding [1]:
> 
>   "Specifications that use QNames to represent URI/local-name pairs
>    MUST describe the algorithm that is used to map between them."
> 
> and the words in the Architecture doc't current draft [2]:
> 
>   "Language designers who use QNames MUST provide a mapping to URIs."
> 
> These actually say _very_ different things -- the first 
> requires me to tell you how to identify a binding for the 
> prefix of a QName, but does _not_ require me to come up with 
> a _single_ URI equivalent to the QName itself, whereas as I 
> read the second, that's what it _does_ require.
> 
> Consider the QName 'a:b' in an XPath expression.  The XPath 
> REC specifies carefully how to convert this to a 
> URI/local-name pair, but it does _not_ specify a mapping to 
> URIs, because it _can't_.  If the XPath expression concerned 
> is, in its entirety
> 
>    "//*[@a:b]"
> 
> what could such a URI possibly be?
> 
> I trust this is just an oversight, and the intent was for the 
> Arch Doc't to reproduce the finding -- if so, an exact 
> reproduction of the wording of the finding would reduce the 
> potential for confusion.
> 
> ht
> 
> [1] http://www.w3.org/2001/tag/doc/qnameids.html
> [2] http://www.w3.org/2001/tag/2003/webarch-20031128/#xml-qnames
> -- 
>   Henry S. Thompson, HCRC Language Technology Group, 
> University of Edinburgh
>                       Half-time member of W3C Team
>      2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 
> 131 650-4440
> 	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
> 		     URL: http://www.ltg.ed.ac.uk/~ht/
>  [mail really from me _always_ has this .sig -- mail without 
> it is forged spam]
> 
Received on Wednesday, 3 December 2003 09:29:44 GMT

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