W3C home > Mailing lists > Public > public-rdf-in-xhtml-tf@w3.org > August 2007

Re: Clarifying CURIEs [was Re: RDFa - Dublin Core Metadata - [Fwd: Draft of revised version of Expressing DC in X/HTML meta/link elements]]

From: Ivan Herman <ivan@w3.org>
Date: Fri, 10 Aug 2007 09:57:50 +0200
Message-ID: <46BC1A7E.3030600@w3.org>
To: Dan Brickley <danbri@danbri.org>
CC: Niklas Lindström <lindstream@gmail.com>, Mark Birbeck <mark.birbeck@formsplayer.com>, W3C RDFa task force <public-rdf-in-xhtml-tf@w3.org>

Dan Brickley wrote:
> Ivan Herman wrote:
>> Niklas,
>> I share your uneasiness, and I agree that the acceptance of the
>> rel="dc.creator" type of mechanism is less clean. But we have to face
>> realities (and, with all my respect to Ian and eRDF, this has nothing to
>> do with eRDF!). The fact of the matter is that the
>> <link rel="dc.copyright" href="blabla"/>
>> type of markup in HTML pages to include basic DC terms have become very
>> widespread indeed. To take an example, this is what the W3C home page
>> uses:-) Of course, those can (and are) understood and interpreted by
>> GRDDL, but I think it would be a shame if an RDFa processed XHTML file
>> did not understood those perfectly valid metadata or, as the DCMI
>> document and mail I forwarded, the DCMI recommendations decided to
>> ignore RDFa.
> I don't know. We still get a *lot* of grief for RDF/XML having so many
> syntactic variants, which were added in 97/8 each for fine reasons. RDFa
> is already complex; the more we add, the harder it is going to be to
> learn. We always also have GRDDL to fall back on. Could GRDDL be
> involved by citing the XSLT from the documents that the link/rel/href
> constructs point to?

Of course. As I say, the W3C home page uses that mechanism, as well as
an XSLT to produce an RSS feed...

> Before changing RDFa here, I'd like to know: 1. just how many documents
> are we talking about 

Well, this is what the DCMI currently proposes, ie, potentially a lot.


We could of course convince them to use the RDFa notation but I am not
sure that will happen.

>                        2. how many of them are XHTML 3. whether the
> resulting RDF would be any good. For example, there is no such thing as
> dc:copyright or dc.copyright (dc:rights is the closest).

Dan, this was just the example I put in writing the mail! Forget about
the details, call it dc.blabla!:-)

>> Dublin Core is not the only metadata that uses this mechanism. For
>> example, if I use OpenID, I am supposed to add the following <link>
>> elements into my HTML header (that I can then use as my OpenID URI):
>> <link rel="openid.server" href="http://pip.verisignlabs.com/server" />
>> <link rel="openid.delegate"
>> href="http://ivanherman.pip.verisignlabs.com/" />
>> It would be a perfectly o.k. to have RDF statements on your page on
>> openid, but we hit the same traditional data format!
> It is (I guess, can't promise :) not too late for the OpenID community
> to adopt and evangelise a more modern syntax. But to be fair, RDFa isn't
> finished yet, so we can't blame them for using a more "traditional" format.

Yes, exactly:-)

>> However, there is an alternative to make the pill less bitter. We can:
>> accept the 'dot notation' as an alternative to the 'coloumn notation' in
>> the <head> only, ie, essentially for <link> and <meta> elements only.
>> These would allow RDFa to include the traditional metadata formats.
> The seems healthy (perhaps also mark it explicitly "for backwards
> compatibility" or even deprecated?

O.k. I can perfectly live with this; actually, I do think this is indeed
better and cleaner than what I originally said. I hereby change my
position:-) and keep it to the <head> only!

>> None of these create any implementation problem. As I am in an
>> implementation mood these days:-) I could add these features to my
>> implementation in about 30 minutes (with testing) without any particular
>> problem, and a change to the alternative above would not be an issue
>> either. But I do not think ignoring the issue is good for us.
> Changes to parsers aren't the only cost. We also have to think about
> people learning to read this stuff. Any new rule is still a new rule.

Sure. But with the caveat of marking it as 'deprecated' I think we can
live with it...


> cheers,
> Dan
>> My two pence...
>> Thanks
>> Ivan
>> Niklas Lindström wrote:
>>> Hello!
>>> This is regarding the alternative mechanisms of a "dot-notation"
>>> shorthand and namespace binding by "schema.*" ("schema-dot"). It
>>> really bakes my noodle. :)
>>> Doesn't this amount to the incorporation of eRDF into RDFa? While that
>>> *may* be fortunate (since eRDF is in use today), something makes me
>>> feel very uneasy about it. I think it introduces a bit of
>>> arbitrariness at the core, which among other things (probably) makes
>>> it harder to learn.
>>> In my opinion, eRDF is a competent but less powerful alternative to
>>> RDFa, with different (though quite overlapping) sets of features and
>>> trade-offs. Although eRDF works with HTML 4.01 and RDFa does not
>>> (right?), which could merit this, I'd still like to stay on the XHTML
>>> side of things. Having the current syntax for CURIEs and namespace
>>> declarations as the only one is a big part of that IMHO.
>>> While having RDFa capable of coexisting with microformats (and eRDF)
>>> is a goal, I see this as legacy compatibility (I would never mix them
>>> if I could avoid it). If needed, GRDDL.
>>> What is left is how to handle e.g.:
>>>     <link rel="dc.creator" href="http://example.org/Fred" />
>>> I felt a little chill thinking about it (reminiscing the issues with
>>> mingling of values in @class when it was the proposed rdf:type
>>> shorthand). Would this lead to the generation of a nonsensical triple
>>> by today's rules? It is of course directly related to the issue of how
>>> to handle non-prefixed names. I have silently discarded it with a
>>> thought like "nah, non-prefixed names will be ignored", but that
>>> hasn't been resolved, has it? Nor what happens when undeclared
>>> prefixes are used?
>>> I think of RDFa as a pristine approach. If reasonable, as mentioned
>>> above, all kinds of things should peacefully coexist without any
>>> meaning to RDFa (hence the exclusion of @class value parsing). But
>>> @rel="dc.creator" is definitely too close to home to be left
>>> unconsidered. As is:
>>>     <link rel="schema.dc" href="http://purl.org/dc/elements/1.1/" />
>>> ; a mechanism which looks very odd to me in an RDFa context (too
>>> ad-hoc, for one; raising nesting/scope issues as well).
>>> I think I'd prefer if these constructs just aren't meaningful in the
>>> RDFa sense. eRDF is for GRDDL, as I see it.
>>> I am very open to more debate though (and this is a real issue). The
>>> thing to really consider is that if "dot-notation" is interpreted but
>>> the "schema-dot" namespace declaration is *not*, the handling of
>>> undeclared prefix usage is of utmost importance ('schema'..). And if
>>> none is of meaning, how shall non-prefixed values in @rel/@rev work?
>>> (I might actually end up *supporting* this for pragmatic reasons. But
>>> only with a desire to explicitly state that it would be for legacy
>>> reasons and discouraged when authoring new XHTML+RDFa. I'm in need of
>>> more convincing though.)
>>> [Side-note: If non-prefixed names in @rel/@rev *do* mean "default
>>> namespace + name", wouldn't that -- since that namespace is almost
>>> invariably <http://www.w3.org/1999/xhtml> -- lead to inadvertent
>>> references to an unmanaged set of URIs all beginning with
>>> "http://www.w3.org/1999/xhtml"? For this alone, I vote for ignoring
>>> them. Allowing ":somename" - perhaps. At least it would be (more)
>>> intentional. My guess is that many host language namespaces for RDFa
>>> will not also be RDF vocabularies. Predefineds like @rel="alternate"
>>> in (x)html is another thing I think. Are they even concepts prefixed
>>> by the xhtml syntax namespace? That's reasonably another debate
>>> though.]
>>> Best regards,
>>> Niklas
>>> On 8/9/07, Ivan Herman <ivan@w3.org> wrote:
>>>> O.k. That is actually in line with what I said and done. I always
>>>> referred to the value of @rev, @rel, @property, @instanceof as 'sort
>>>> of'
>>>> qnames, and I think what I meant is (and the way I implemented it) is
>>>> exactly what you say: I split the string at the ':' point, take the
>>>> left
>>>> part as an index into an associative array ('dictionary' in Python
>>>> speak) and simply concatenate the value with what is on the right hand
>>>> side of ':'. Adding an alternative branch which does that for '.'
>>>> instead of ':' is a piece of cake (and I have already added it to the
>>>> code locally...:-)
>>>> However. We clearly would need proper TF resolution on these issues.
>>>> Thanks Mark
>>>> I.
>>>> Mark Birbeck wrote:
>>>>> Hi Ivan,
>>>>> We might as well start another thread. :)
>>>>> The CURIEs spec is not actually about the square bracket stuff--that's
>>>>> just a way to disambiguate between a CURIE (compact URI) and a URI.
>>>>> The idea of CURIEs is that instead of using QNames as a URI
>>>>> abbreviation syntax, we use something that is specifically designed
>>>>> for the job. The problem with the definition of 'QName' is that it is
>>>>> essentially about defining element and attribute names in XML:
>>>>>   <a:b c:d=:x" />
>>>>> However, over the years QNames have been used to abbreviate URIs
>>>>> (RDF/XML) and to namespace various features like functions (XPath) and
>>>>> data types (XML Schema). At least those uses are inside XML documents,
>>>>> but the use of QNames in SPARQL is genuinely odd, since it has nothing
>>>>> to do with XML.


Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Friday, 10 August 2007 07:57:52 UTC

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