- From: Mark Birbeck <mark.birbeck@x-port.net>
- Date: Mon, 19 Jun 2006 13:07:40 +0100
- To: "Ian Davis" <iand@internetalchemy.org>
- Cc: "Karl Dubost" <karl@w3.org>, "public-rdf-in-xhtml task force" <public-rdf-in-xhtml-tf@w3.org>
Hi Ian, > Actually this thread doesn't concern eRDF at all. What I'm interested in > is why RDFa uses qnames, which I've shown to be fragile... I think that's stretching things, to put it bluntly! Each of the 'problems' you have raised I've shown to actually not be problems. I agree that QNames in XML is quirky, and I don't think you'll find many people to disagree with that. But it's an enormous leap to suggest not using something as widespread and standard as QNames, and any alternative would have to be extremely well worked through and consistent, and not something that just evolves. >... when the > following would work just as well and be robust when used with all > current XML tools: > > <span property="http://purl.org/dc/elements/1.1/date" > type="http://www.w3.org/2001/XMLSchema#date" > content="2006-01-02"> I agree with you here Ian, I really do. Indeed, Steven Pemberton had to persuade me away from exactly this approach many moons ago in our early work on RDFa! But one of our 'communities' (as Karl rightly pointed out) is HTML authors, and we really can't expect them to do this. I know the approach you describe has been successfully used in Atom, but those documents are invariably generated rather than being hand authored. It's no accident that RDFa aims to be friendly to the community of HTML authors. Getting access to the metadata that this 'community' puts into their documents has been a primary motivation for RDFa since the beginning. Here's a quote from the introduction to one of the early drafts, February 2004 (it was called RDF/XHTML back then): We have two standards running parallel with each other; HTML is the de facto standard for document markup, accounting for millions of items on the web. RDF is a standard for expressing metadata, which in turn provides a foundation for making use of that metadata, such as reasoning about it. Yet the former is very rarely the subject of the latter; meta information placed in the HTML family of documents is often encoded in such a way as to make it difficult to extract by RDF-related parsers. And if it cannot be extracted, then it cannot be used. Our intention here is to make more of the information that is contained within HTML-family documents available to RDF tools, but without putting an unnecessary burden on authors familiar with HTML, but not with the subtleties of triples and statements. [1] The final paragraph is probably key to the whole concept--it was being suggested that we make the metadata in documents availabled to RDF tools "but without putting an unnecessary burden on authors". This is not just us being nice; it was a recognition that unless it is easy to put metadata in documents, authors won't do it. So, let's back up a little, and say that we would probably agree *some* URI prefixing/abbreviation mechanism is desirable, but we lets say that we don't quite know what it might be yet. I've proposed CURIEs as a QName-like syntax, that uses XML namespaces as its source of subsitution values. On a number of occassions myself and others have discussed making this proposal open enough to cope with other substitution mechanisms: so for example SPARQL could use CURIEs but stipulate that its 'PREFIX' syntax is used to provide the strings for subsititution; Misha and the IPTC could provide an additional attribute in NewsML to provide the substitution strings, perhaps via some external file; and yes, we could even support some other mechanism than XML namespaces in XHTML to provide the substitution strings. But although I've done quite a lot of work in this area, try to make CURIEs open in a similar way to that of XPath (which defines a 'context'), that doesn't necessarily mean that I think that XHTML should use a mechanism other than namespaces! ;) What I *am* getting at, though, is that if we successfully made CURIEs open enough that it could support other syntaxes and methods of substitution (in the way Misha would like), then if we do decide to make 'the big change' in RDFa (i.e., to not use XML namespaces), then it would just be a case of flicking a switch and using a different 'context' in CURIEs. To put it a different way, we should try to crack the problem 'in the abstract', since we know that regardless of our final decisions on using QNames/CURIEs in XHTML, there are at least two groups that cannot use namespaces as their source of 'string substitutions'--the IPTC and those not using XML. If they are to be able to use CURIEs then we've got to solve the problem anyway, and once we've solved the problem we can separately make a decision as to whether to use the same technique ourselves in RDFa/XHTML. Regards, Mark [1] http://www.formsplayer.com/notes/xhtml-meta-data-03.html -- Mark Birbeck CEO x-port.net Ltd. e: Mark.Birbeck@x-port.net t: +44 (0) 20 7689 9232 w: http://www.formsPlayer.com/ b: http://internet-apps.blogspot.com/ Download our XForms processor from http://www.formsPlayer.com/
Received on Monday, 19 June 2006 12:07:54 UTC