Aryeh Gregor wrote:
RDFa is a way to embed data in HTML more robustly than with attributes like class and title, which are reserved for author use or have existing functionality. It allows you to specify an external vocabulary that adds some semantics to your page that HTML is not capable of expressing by itself.
More to the point, it allows an RDF graph to be overlaid onto an XHTML document so that the XHTML document and the RDF graph can share some strings. The XHTML data model isn't extended per se. Instead, a separate RDF graph can be extracted.
Both RDFa+HTML and Microdata are Working Drafts at the W3C right now
It's true that both HTML+RDFa and Microdata have been published in Working Drafts at the W3C. However, Microdata has never been through a Working Group Decision to publish as a First Public Working Draft while HTML+RDFa has. Microdata was added to a Working Draft after FPWD and there has since been a Working Group decision to take Microdata out of that spec.
It is reasonable to expect that soon HTML+RDFa and Microdata could be in the same stage Process-wise, but it's inaccurate to portray them as being at the same stage Process-wise right now.
I should note that currently Google and a couple of others support RDFa but not Microdata.
See http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2009Sep/0126.html (search for the word "deviate").
Manu Sporny wrote:
The general points that you made were riddled with technical inaccuracies, bad advice, and if implemented by the MediaWiki community, would have resulted in semantic data that would have been ambiguous at best and erroneous at worst.
With that introduction, I think it's fair to evaluate your message for inaccuracies or relevant omissions as well.
The above could be marked up in RDFa, with pre-defined vocabs, like so:
It should be noted that the concept of "pre-defined vocabs" is neither in the HTML+RDFa draft nor in the RDFa in XHTML spec from the XHTML2 WG.
<p about="EmeryMolyneux-terrestrialglobe-1592-20061127.jpg" typeof="dctype:StillImage"> <span property="dc:title">Emery Molyneux Terrestrial Globe</span> by <a rel="cc:attributionUrl" href=" http://example.org/bob/"
property="cc:attributionName">Bob Smith</span>is licensed under a <a rel="license" href=" http://creativecommons.org/licenses/by-sa/3.0/us/"
Creative
Commons Attribution-Share Alike 3.0 United States License</a>.</p>
Hiding the CURIE declarations is a common pattern when advocating RDFa: It makes RDFa appear tidier than it is. To write this in RDFa in XHTML (the RDFa spec you say is safe to use for deployment), one would need to declare the CURIE prefixes:
<p xmlns:dctype="http://purl.org/dc/dcmitype/" about="EmeryMolyneux-terrestrialglobe-1592-20061127.jpg" typeof="dctype:StillImage"> <span xmlns:dc="http://purl.org/dc/elements/1.1/" property="dc:title">Emery Molyneux Terrestrial Globe</span> by <a xmlns:cc="http://creativecommons.org/ns#" rel="cc:attributionUrl" href=" http://example.org/bob/"
property="cc:attributionName">Bob Smith</span> is licensed under a <a rel="license" href=" http://creativecommons.org/licenses/by-sa/3.0/us/"
Creative
Commons Attribution-Share Alike 3.0 United States License</a>.</p>
Philip Jägenstedt already covered other points about the examples.
However - XHTML1+RDFa is a published W3C Recommendation and it is safe to use it for deployment.
RDFa in XHTML has indeed been published as a Recommendation jointly by the Semantic Web Deployment Working Group and the XHTML2 Working Group. However, you fail to mention that even though the document mentions "HTML" in its first sentence, all the normative matter concerns strictly XHTML and the document has gone through the W3C Process as a specification that applies to XML.
MediaWiki uses the text/html and, thus, its pages get processed as HTML, so it would be inappropriate to rely on a spec that had been reviewed as an XML spec.
I think it's misleading to promote text/html deployment of specs whose normative matter has been written and reviewed for XML. The most egregious example of this is that the XHTML2 WG has written the normative matter of XHTML 1.x specs for XML but then published a Working Group Note (Notes can be pretty much anything and don't go through the W3C Recommendation track Process) that gives advice on deployment as text/html (http://www.w3.org/TR/xhtml-media-types/).
Furthermore, the ease of getting a spec to REC at the W3C depends on how many people are interested in the spec. The more people are interested in a spec, the more review comments there are. The flip side is that when there's *less* interest in a spec, it's easier to get it to Recommendation due to fewer comments raised. Thus, progress along the REC track isn't a commensurable indicator of technical merit or technical maturity across different specs and WGs.
Also, when assessing the "safe" deployability of RDFa in XHTML, it's relevant to consider that 1) RDFa in XHTML was knowingly (see http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2008-August/015913.html) progressed on the Recommendation track without resolving how RDFa works with HTML first. 2) An RDFa 1.1 is in the works, and the changes being considered make RDFa 1.0 look like a beta release. (Which is understandable, since a good part of the technical review of RDFa has occurred after RDFa in XHTML was rushed to REC.)