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

Re: Fine-tuning CURIEs

From: Ivan Herman <ivan@w3.org>
Date: Tue, 11 Sep 2007 17:04:12 +0200
Message-ID: <46E6AE6C.2070407@w3.org>
To: Mark Birbeck <mark.birbeck@formsPlayer.com>
Cc: W3C RDFa task force <public-rdf-in-xhtml-tf@w3.org>

I have given some thoughts but, after all, I decided to vote against
your proposal. Sorry about that:-)

The main issue I have is to avoid the generation of 'accidental'
triples. The @rel attribute is not proper to RDFa and may and is used in
other places in an XHTML file. The intention may _not_ be the generation
of a triple but, in the scheme your propose, there is no way to avoid
that. Eg, the <link> element use rel for a stylesheet; I am not sure it
is relevant to generate a triple for the CSS file (certainly not without
the user asking us to do it).

Ie: a:b and :b are, in my view, the only two forms that we should accept...


Mark Birbeck wrote:
> Hello all,
> During the course of finishing off the Syntax document a couple of
> issues have popped up. I'll deal with them in separate threads.
> This thread relates specifically to the way that we ensure that
> mark-up like this yields the kind of triples we'd expect:
>   <link rel="next" href="o" />
> At the moment we say that some kind of preprocessor runs and that the
> mark-up above is 'mapped' to this:
>   <link rel="xh:next" href="o" />
> This is fine, and if we're happy with that, we can just leave it.
> However, there is another way to come at this, which I'll describe.
> Myself and Shane changed the CURIE definition recently so that *both*
> the prefix and the colon were optional:
>   [ [ prefix ] ':' ] reference
> This is so that all of the following are valid:
>   a:b
>   :b
>   b
> We did this because the second format is needed in N3 and Turtle-based
> languages such as SPARQL, whilst the third format is needed if we want
> to be able to handle legacy QNames.
> I was therefore looking more closely at what exactly these three
> different formats should mean since we don't have that defined clearly
> in our specification. The most obvious route for the second format is
> to say that it should use the current default namespace, making it
> consistent with SPARQL, etc.
> However, there is no general practice for non-prefixed QNames--in some
> situations the default namespace is used (such as in declarations of
> type in XML Schema), and in some situations it is explicitly ignored
> (such as when defining a template in XSLT). This means that we could
> choose to use the default namespace, or define some other rule like
> always using the XHTML namespace, or even the current value of [base].
> An interesting thing comes about though, if we were to choose to use
> the default namespace; returning to the syntax we had earlier:
>   <link rel="next" href="o" />
> we could obtain a predicate of 'xh:next' without having to do _any_
> preprocessing, but *only* if the default namespace was XHTML:
> <html xmlns="http://www.w3.org/1999/xhtml">
>   <head>
>     <title>...</title>
>     <link rel="next" href="o" />
>   </head>
>   ...
> </html>
> I like this approach since I think it gives future authors a lot of
> flexibility. It also, quite by accident, provides a way to remove the
> need for a lot of the preprocessing we have been discussing. For
> example, one could mark-up OpenID using a layout like this:
>    <link rel="openid.server" xmlns="http://openid.net/"
>       href="https://api.screenname.aol.com/auth/openidServer" />
>    <link rel="openid.delegate" xmlns="http://openid.net/"
>        href="http://openid.aol.com/wezfurlong" />
> Note that instead of worrying about trying to make "openid." into some
> kind of prefix, we simply use the full string as the reference.
> Anyway, there you have it. The choices seem to be:
>   * have a preprocessing step to get at 'legacy' properties and
> short-forms, such
>     as xh:next. In this case we'd still need to say what unprefixed CURIEs mean,
>     but wherever we choose would make no difference to the preprocessing step;
>     they could be in the default namespace, the current document, or some explit
>     namespace;
>   * or, we say that CURIEs with no prefix--with or without the
> colon--use the default
>     namespace, and then leverage this to cope with some of the legacy properties
>     like 'xh:next' and 'openid:openid.delegate' _without_ the need for
> a preprocesing
>     step.
> Myself, I can go either way; I'd prefer the second solution, since I
> think it would be quite neat if we only used the preprocessing step
> when it is really necessary. This is because although the
> preprocessing seems pretty benign, we've never really discussed things
> like the fact that the preprocessor must operate across all of the
> attributes, in a consistent way. For example, the value of 'next'
> would need mapping in both @rel and @about, for the following
> statements to work:
>   <html xmlns:skos="http://www.w3.org/2004/02/skos/core#">
>     <head>
>       <link rel="next" href="o" />
>       .
>       .
>       .
>       <div about="[next]" instanceof="skos:Concept">
>         <span property="skos:prefLabel">Next</span>
>         <div property="skos:definitionl">
>           Refers to the next document in a linear sequence of documents. User
>           agents may choose to preload the "next" document, to reduce the
>           perceived load time.
>         </div>
>       </div>
> However, if the CURIEs were using the default namespace you can see
> that this mark-up would 'just work'.
> Your thoughts and votes please. :)
> Regards,
> Mark


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 Tuesday, 11 September 2007 15:04:13 UTC

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