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Re: URIs in @rel and @property...

From: Ivan Herman <ivan@w3.org>
Date: Mon, 16 Nov 2009 13:03:51 +0100
Message-ID: <4B013FA7.3050702@w3.org>
To: Ben Adida <ben@adida.net>
CC: RDFa <public-rdf-in-xhtml-tf@w3.org>
Still following up on this...

Ben Adida wrote:
> Hey folks,
> I'm catching up on the minutes from today, looks like a productive
> meeting, very nice.
> I am a little bit concerned about supporting plain CURIEs in @about,
> @href, and @resource. For one, the use case is *very* limited, since the
> whole point of prefixes is to reuse vocabularies, and that applies to
> predicates, not to subjects and objects. Also, we want to continue to
> support relative URIs in @about, just like @href (and the spec for @href
> isn't about to change), and that's not very easy to do if we allow plain
> CURIEs, too.

- I agree that we should _not_ touch @href (and @src). Those are not
under our control, they should stay as they are.

- I must admit I did not see your comment on 'that applies to
predicates, not to subjects and objects' until now. And I do not agree
with that. Apart from the few examples I gave in my previous mail,
another one just came to my mind: one of our use case is to provide a
readable version of a vocabulary definition. Such description will be
full of subclass, subproperty etc relationships on its own domain, ie,
both the subject and the object part will need curies-s. And protected
curie-s are a pain and are error prone...

- I actually did an implementation on my machine, reasonably tested. The
algorithm is fairly simple (unless I miss an elephant in the room):

1. check whether the value is of the 'a:b' form and 'a' is defined CURIE
2. if yes, return the URI as defined by the CURIE
3. if not, do a urljoin of the base URI and the value. Per definition of
that join, if the value is an absolute URI, that will prevail, otherwise
the urljoin rules will dictate the behaviour. (eg, Python has just
method as part of its standard library...)

The only difference between the old and new version is entries #1 and
#2, #3 was the behaviour as of RDFa 1.0.

Actually, the same steps could also be used for @rel/@rev/@typeof, ie,
allowing relative URIs for those attributes as well! Which might
simplify everything: all RDFa attributes would behave similarly. (Again,
we should not touch @href and @src.)

So is there an elephant?:-)


> So I think we should be as conservative as possible with this change.
> Allowing absolute URIs in @rel, @property, @typeof, and @datatype makes
> sense, but generalizing the "other way" to let @about and @resource (and
> @href) carry plain CURIEs does not, in my opinion, because of important
> existing uses for those attributes.
> -Ben


Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
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Received on Monday, 16 November 2009 12:04:20 UTC

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