Hi All,
I've been taking a closer look at microdata. While I like the proposal
in general, in particular the chance to unite microformat style
annotations with some of the Semantic Web formalism (such as URIs for
objects), there are still a number of points that I feel could be
improved. So here are my proposals for discussion:
#1
The use of a URI as the value of the id attribute. It seems to me there
is actually nothing in the spec that would stop this:
"Identifiers are opaque strings. Particular meanings should not be
derived from the value of the id attribute."
This is great because in principle I could do something like:
<section id="http://john.example.com#hedral";
item="org.example.animal.cat com.example.feline">
<h1 itemprop="org.example.name com.example.fn">Hedral</h1>
</section>
I assume you can achieve something similar with the "about" property but
that would require me to write:
<section item="org.example.animal.cat com.example.feline">
<h1 itemprop="org.example.name com.example.fn">Hedral</h1>
<a itemprop="about" href="http://john.example.com#hedral"/>
</section>
This is longer by itself, and if I want an internal identifier as well,
than I have to write:
<section id="hedral" item="org.example.animal.cat com.example.feline">
<h1 itemprop="org.example.name com.example.fn">Hedral</h1>
<a itemprop="about" href="http://john.example.com#hedral"/>
</section>
#2
The other area that could be possibly improved is the connection of type
identifiers with ontologies on the web. I would actually like the notion
of reverse domain names if
-- there would be an explicit agreement that they are of the form
xxx.yyy.zzz.classname
-- there would be a registry for mappings from xxx.yyy.zzz to URIs.
For example, org.foaf-project.Person could be linked to
http://xmlns.com/foaf/0.1/Person by having the mapping from
org.foaf-project to http://xmlns.com/foaf/0.1/.
It wouldn't be perfect, the FOAF ontology as you see is not at
org.foaf-project but at com.xmlns. However, it would be a step in the
right direction.
#3
I would consider adding the sameAs property as part of the standard
vocabulary. This is a term from the OWL vocabulary that is widely used
in the Linked Data world for connecting entities that are deemed to be
equivalent. Alternatively, we could add the entire RDFS and OWL
vocabulary to the spec.
#4
I don't expect that writing full URIs for property names will be
appealing to users, but of course I'm not a big fan either of defining
prefixes individually as done in RDFa with the CURIE mechanism. Still,
prefixes would be useful, e.g. foaf:Person is much shorter to write than
com.foaf-project.Person and also easier to remember. So would there be a
way to reintroduce the notion of prefixes, with possibly pointing to a
registry that defines the mapping from prefixes to namespaces?
<section id="hedral" namespaces="http://www.w3c.org/registry/";
item="animal:cat">
<h1 itemprop="animal:name">Hedral</h1>
</section>
Here the registry would define a number of prefixes. However, the
mechanism would be open in that other organizations or even individuals
could maintain registries.
Looking forward to your feedback,
Peter
