- From: Julian Reschke <julian.reschke@gmx.de>
- Date: Fri, 10 Jul 2009 19:50:25 +0200
- To: Mark Birbeck <mark.birbeck@webbackplane.com>
- CC: RDFa <public-rdf-in-xhtml-tf@w3.org>
Hi Mark, thanks for doing this work. You know I'm not happy with anything that leaves ambiguity, but it certainly is a step into the right direction. Some comments in-line. Mark Birbeck wrote: > ... > FALSE POSITIVE CURIES > > The scenarios that seems to be causing concern is that when a URI > begins with the same string as a prefix mapping, it creates a 'false > positive' CURIE. > > Using Julian's example: > ... I think it was Sam's... > ... > The problem with this example is that it is relying on a situation > that won't arise to make its point; as RDFa stands at the moment, why > would anyone place a URI into the @rel or @rev attribute? Nothing in > the spec gives the impression that URIs are valid in @rel, and no > other host languages seem to indicate this either. > ... But then the host languages do not disallow it either. > ... > This creates a lot of extra work, and in particular makes > cut-and-paste examples more difficult. An obvious question then is why > RDFa doesn't simply support this kind of mark-up: > > <div about="#me" typeof="http://xmlns.com/foaf/0.1/Person"> > <a rel="http://xmlns.com/foaf/0.1/knows" > href="http://www.w3.org/People/Ivan/#me" > >Ivan Herman</a> > </div> > ... Indeed! > WAY BACK... > > This is a pretty obvious technique, so it probably won't surprise > anyone that it was considered...way back. :) > > The problem we had at the time we discussed this was that if we went > for URLs in @rel, then we'd need to go for safe-CURIEs also. And that > then raised problems with the pre-existing tokens from HTML > ... Interesting... > ... > The issue is, how would we know when we had a relative path, and when > we had a reserved value: > > @rel="next" > > @rel="relative-url" > ... Could you elaborate on why this matters? > At the time, the only solution we could think of was to insist on > safe-CURIEs for all non-URI values: > > @rel="[next]" > > @rel="[dc:rights]" > > @rel="relative-url" Why not simply state that something that looks like an absolute URI/IRI *is* one, and that everything else is a token? > ... > DIFFERENTIATING BETWEEN CURIES AND URIs > > Interestingly enough, it is possible to solve this problem, by simply > saying that any string of characters that begins with a predefined > prefix is a CURIE, and anything else is a URI. > ... With the caveat that this is a bit fragile, because the semantics of a @rel value can be broken by a change somewhere else in the document. > This is quite a different approach to the one normally taken to > differentiation. The usual discussion is to say that it's impossible > to tell if: > > x:y > > is a URI or a CURIE because 'x' could be a protocol, and 'y' could be > any part of a URI. It might seem an obvious remedy to say that if 'x' > is a protocol, then treat 'x:y' as a URI. However, this would 'break s/protocol/URI scheme/ > ... > PROPOSAL > > So to bring everything together, the proposal is: > > (a) RDFa should add support for URIs in attributes that currently only > support CURIEs; +1 > (b) authors should be encouraged to use safe-CURIEs in those > attributes; +1 > (c) but since ordinary CURIEs may still be used, we should differentiate > by saying that anything appearing before a colon, that is not a > mapped prefix, is a protocol. +-0; but I understand that going further would break existing content. Now, *technically*, existing content will be in XHTML, not HTML, right? So maybe in the process of defining RDFa-in-HTML, we could go even further than that? > ... BR, Julian
Received on Friday, 10 July 2009 17:51:11 UTC