On Mon, Jan 18, 2010 at 23:34, Manu Sporny <msporny(a)digitalbazaar.com> wrote:
You cannot, however, express RDF fully in Microdata -
it is impossible
in cases where it matters to Wikipedia (like data-typing).
I'm not a Wikipedia developer or particularly active editor, but it
sounds quite doubtful that XML Schema Datatypes matters to Wikipedia.
Perhaps I haven't understood RDFa, but surely the vocabulary must
define the datatype? If not, is @datatype a mandatory attribute that
just adds dead weight all over the place? And if vocabularies do
define the datatypes, why do you need to override them?
I do also think that Microdata has made several really
big mistakes that
we made in the Microformats community that were corrected in the RDFa
community. Namely, not using CURIEs and adding the requirement that all
URLs are repeated as many times as they're used. It's fine as an option,
but not that great if one has to repeat a URL 50 times in a web page...
which Wikipedia will eventually have to do if it is using Microdata.
There are other solutions to the "URLs are long" problem than prefix
schemes. Incidentally http://n.whatwg.org/work
is rather short, and I
hope future vocabularies will have the good taste to use even shorter
That's provably false. Microdata vocabulary
validation is hard-coded in
the specification. Dan Brickly and Ian Hickson had an IRC conversation
about just this today. In order to validate Microdata, you must first
either convert it to RDF and even if you do, it will fail attempts to
validate the literals that should have a datatype.
Is the only kind of validation that RDF provides validation that
something is the same kind of data it claims to be? That sounds
similar to and as unhelpful as doctypes. What if the author doesn't
set the datatype?
If you want a
Microdata vocabulary validator, you have to create one for each
vocabulary... just like we had to do in the Microformats community,
which some of us now recognize as a catastrophic mistake.
RDFa, via RDF, allows arbitrary data validation - one validator with any
number of vocabularies. Microdata does not allow arbitrary validation -
there must be one hard-coded validator per vocabulary.
What are the exact mechanisms here? Does a RDFa validator dereference
all predicates and try to get an RDF Schema to validate against?
Doesn't that destroy any web server which hosts schemas for popular
vocabularies (like with W3C doctypes)? On the other hand, if only the
document itself is used, what kind of validation can be meaningful?
In any case, validators for microdata is something to be worked on,
but I don't think either dereferencing vocabulary URLs or an official
schema language is likely to be part of the solution (the latter
because you need a full programming language to validate certain types
of data, not just grammar rules).