W3C home > Mailing lists > Public > public-rdf-in-xhtml-tf@w3.org > November 2005

Re: CURIEs vs. QNames

From: Norman Walsh <Norman.Walsh@Sun.COM>
Date: Mon, 28 Nov 2005 12:21:53 -0500
To: Ben Adida <ben@mit.edu>
Cc: Dan Connolly <connolly@w3.org>, public-rdf-in-xhtml-tf@w3.org
Message-ID: <87irucpu1a.fsf@nwalsh.com>
/ Ben Adida <ben@mit.edu> was heard to say:
|> | Do I really need to write the Dublin Core URI multiple times?
|> That would work.
| Yes, it would "work," but it would violate one of our strong
| requirements that we help users not duplicate data unnecessarily. If
| a user wants to upgrade from one version of Dublin Core to the next,
| he shouldn't have to go change all the Dublin Core properties used
| throughout every document.

Interesting. I'm used to the argument that URIs are bad because
they're long and hard to type. Your argument above is for a level of
indirection, is that right?

|> I'd prefer to simply allow
|>   <dc:creator>Norman Walsh</dc:creator>
| Seems like <meta property="dc:creator">Norman Walsh</meta> is close
| enough, though again that violates the TAG and overloads the QName
| usage. We're trying to fix that.

The relevant TAG finding says:

  | In so far as the identification mechanism of the Web is the URI and
  | QNames are not URIs, it is a mistake to use a QName for identification
  | when a URI would serve.

On the face of it, that would argue for

<meta property="http://purl.org/dc/elements/1.1/creator">Norman Walsh</meta>

which certainly avoids the problem. But I understand that's problemtic
for you. The finding goes on to say:

  | That said, the TAG recognizes that there are sometimes pragmatic
  | reasons for chosing short, lexical representations of more complex
  | names and accepts that QNames are an established mechanism for doing
  | so.

So if you need short names, the finding actually suggests using

  | Where there is a compelling reason to use QNames instead of URIs for
  | identification, it is imperative that specifications provide a mapping
  | between QNames and URIs, if such a mapping is possible.

For RDF, I believe the established mapping is "concatenation".

  | Finally, we observe that a whole class of interpretation problems can
  | be avoided if the use of QNames can be restricted to contexts where
  | their identification is natural and unambiguous (element and attribute
  | names, simple content of type xs:QName, etc.) and we encourage
  | developers to employ such restrictions wherever possible.

If the property attribute (and other places where QNames occur in your
syntax) contains only a QName, then I don't think there's anything
wrong with using a QName there. You certainly don't have to invent
something new to satisfy the spirit of the TAG finding.

|> | Do I
|> | really need to start using XSLT just so I can define URI
|> | abbreviations? Or should I simply violate the TAG's recommendation
|> | that QNames not be used as URI abbreviations,
|> Yes. That's what everyone else does, that's what everyone expects.
|> Doing something else is going to be more confusing.
|> | and then be stuck with
|> | a mostly-working-but-not-quite-complete abbreviation scheme?
|> Yes.
| I feel that the above approach is deeply broken. You're effectively
| saying "ignore the TAG, that's what everyone else does." Even worse,
| it seems that we should sometimes ignore the TAG, and at
| other times abide by the TAG rules quite strictly. Maybe this is the
| unwritten W3C rule and I'm just not used to it.

Read section 6 of that finding again. The TAG went out of its way to
frame the architectural principle in a manner consistent with actual,
real-world usage. The finding explicitly grants that there are
sometimes reasons to use QNames and gives guidance on how to
mitigate the problems they cause.

|> | I certainly understand the worries about the specific syntax that
|> | will be used for CURIEs, and the task force is actively discussing
|> | various options right now. However, I don't understand this reaction
|> | to the CURIE concept.
|> Conceptually, I think it's going to be confusing to introduce another
|> syntax for something that can almost always be represented as a QName
|> without introducing a new syntax. Syntactically, I think overloading
|> the QName syntax is just plain wrong.
| So, if I understand you correctly, you're saying there is no right
| solution. The current solution of overloading QNames is syntactically
| (and possibly semantically) wrong. Yet everyone does it. And it
| violates the TAG recommendation. If we continue to live with "almost
| always," confusion will only get worse, and we are going to come up,
| at some point, with a series of scenarios that inevitably don't fit.

The only scenario I recall seeing was the one where the local-name
part of the putative QName is not an NCName. Are there other
scenarios, or is that the only one?

| Why are we afraid to start solving this problem? We have a very good
| reason to address it now. RDF clearly calls for using namespaces
| multiple times, particularly multiple namespaces in a given document.
| That's the point of RDF, in fact. Adding RDF to HTML, where certain
| attributes are already typed as URIs and cannot be changed willy-
| nilly, forces us to resolve the QName/URI conflict.
| The needs of expressing RDF in HTML present an opportunity to solve a
| long-standing problem. I can't see why punting on it yet again is a
| good thing.

Fair enough. I think I've made my points. I won't kibitz any further.
Please let me know when a draft of your proposed solution is

Good luck!

                                        Be seeing you,

Norman.Walsh@Sun.COM / XML Standards Architect / Sun Microsystems, Inc.
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Received on Monday, 28 November 2005 17:51:12 GMT

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