Re: RDFa in HTML5

Hi again,

I also had some thoughts about the general vocabulary usage in your
page. This is a bit more speculative, but I hope it can give you some
ideas.

On Wed, Jan 4, 2012 at 11:08 AM, Augusto Herrmann
<augusto.herrmann@gmail.com> wrote:
> The examples are displayed as (escaped) html code in the rightside
> panel on the following page: http://vocab.e.gov.br/2011/03/vcge
>
> People are meant to copy/paste the code, or just read and undestand,
> in order to learn how to mark up their own pages stating that it's
> about a subject in this controlled vocabulary. That's why we left the
> reference to the page as an empty relative URL (which should resolve
> to whatever address the page is loaded into).
>
> But we also did eat our own dog food: that page also states it's about
> the VCGE controlled vocabulary, by using RDFa 1.1 and Microdata like
> this (lines 21-25):
>
> <!-- Marking up subject using RDFa: the page is about VCGE -->
>  <meta property="http://purl.org/dc/terms/subject"
> content="http://vocab.e.gov.br/2011/03/vcge#esquema" />
>
> <!-- Marking up subject using Microdata: the page is about VCGE -->
>  <meta itemscope itemprop="http://schema.org/about"
> content="http://vocab.e.gov.br/2011/03/vcge#esquema" />
>
> The triple that should be extracted from the RDFa is:
>
> <http://vocab.e.gov.br/2011/03/vcge> dcterms:subject
> <http://vocab.e.gov.br/2011/03/vcge#esquema> .

[See my previous mail for using <link> + @href instead of <meta> + @content.]


In RDFa (1.0 and 1.1) it is explicitly allowed to use several
predicates at once (in @property, @rel and @rev) to provide consumers
limited to certain vocabularies with triples directed specifically
towards them (similarly you can use multiple classes in @typeof). So
to cater both for consumers who only understand schema.org terms and
consumers of Dublin Core, FOAF etc. -- at this stage of the web data
evolution -- it may be good to publish all triples you expect to be
relevant for your intended audiences. E.g. like:

    <link rel="dc:subject foaf:primaryTopic http://schema.org/about"
href="http://vocab.e.gov.br/2011/03/vcge#esquema" />

While this isn't the limited form called Lite, that form of RDFa is
targeted towards *publishers* with limited needs of RDFa. Thus, if
your publishing needs also include consumers of DC and FOAF, and you
don't wish to repeat things, I'd expect this form to be preferable.
(It all depends on the consumer needs and requirements of scalable
usage.)

Notice also that any schema.org predicates and classes can really be
used everywhere. That is, they are possible to use in any RDFa (i.e.
any RDF). Although the schema.org URIs do not resolve to data in RDF
directly (which admittedly is a requirement for proper linked data
vocabularies), schema.org do host an OWL definition of them at [1].
The schema.org ontology doesn't define a semantic equivalence between
e.g. <http://purl.org/dc/terms/subject> and <http://schema.org/about>
though. But it's not unreasonable to expect some relation to that
(and/or foaf:primarySubject), ideally formally stated in the future.
See [2], especially [3] and e.g. [4] for more on that.

RDFa 1.1 specifies a form of vocabulary expansion using a subset of
the OWL semantics at [5], which can be leveraged in different ways
depending both on used vocabularies, and *especially* on the
capability of consumers. Note that this is an *optional* feature of
RDFa 1.1 processors! So don't expect the general search engines to
support these things today. Hopefully though they will come to
understand more vocabulary semantics and interlinking over time, and
also that even more vocabularies and data publishers will leverage
these semantics. This will prevent reinvention and "babelification",
enable reusable and mixable data vocabularies on a general level, and
support generally compatible specialization where needed.

Best regards,
Niklas

[1]: http://schema.org/docs/schemaorg.owl
[2]: http://schema.rdfs.org/
[3]: http://schema.rdfs.org/mappings.html
[4]: http://wiki.dublincore.org/index.php/Schema.org_Alignment/Mappings
[5]: http://www.w3.org/TR/2011/WD-rdfa-core-20111215/#s_vocab_expansion

Received on Wednesday, 4 January 2012 23:58:03 UTC