Re: RDFa in HTML5

Dear Niklas,

2012/1/4 Niklas Lindström <lindstream@gmail.com>:
> 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.

These are very interesting ideas. I've updated the page by using
multiple @property attribute values now, so multiple vocabularies are
used to describe the same property, like this:

<link rel="http://purl.org/dc/terms/subject http://schema.org/about
http://xmlns.com/foaf/0.1/primaryTopic"
href="http://vocab.e.gov.br/2011/03/vcge#esquema" />

This has been done in Microdata as well, as the @itemprop attribute
allows multiple space separated values as well [1]:

<meta itemscope itemprop="http://purl.org/dc/terms/subject
http://schema.org/about http://xmlns.com/foaf/0.1/primaryTopic"
content="http://vocab.e.gov.br/2011/03/vcge#esquema" />

I suppose both of these could be joined into just one tag, but that
wouldn't be a pretty sight.

> [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

Thanks, that's been very helpful. Indeed, using multiple vocabularies
at once is a good practice, at least until user agents start
supporting RDFa Vocabulary Extension.

BTW, I had checked schema.rdfs.org when it came out last year in
response to schema.org, but had no idea it had changed focus like
this, to become a point for learning, examples and support of using
the schema.org vocabulary. Nice!

Best regards,
Augusto Herrmann

[1] http://www.w3.org/TR/microdata/#names:-the-itemprop-attribute

Received on Friday, 6 January 2012 14:29:47 UTC