Re: additionalType property, vs extending Microdata syntax for multiple types

On Mon, Jun 18, 2012 at 6:56 PM, Alexander Botero-Lowry
<alexbl@google.com>wrote:

>
> On Jun 18, 2012 10:48 AM, "Dan Brickley" <danbri@danbri.org> wrote:
> >
> > On 17 June 2012 00:41, Guha <guha@google.com> wrote:
> >
> > > My personal preference is to just add an attribute called type (or
> > > additionalType) which is samePropertyAs rdfs:type and be done with it.
> >
> >
> > I just don't think it's feasible, so let's try to do the best we can
> > with 'additionalType'.
> >
> > A concrete proposal:
> >
> > Property: additionalType
> > samePropertyAs: rdf:type
> > description: "An alias for the rdf:type relationship between something
> > and a class that the thing is in. It is generally preferable to use
> > syntax-native typing mechanisms. The additionalType construct can be
> > useful in constrained syntaxes - e.g. microdata - where multiple types
> > from
> > independent vocabularies cannot be easily expressed. In such
> > situations, care should be taken to assign the most relevant
> > schema.org type using
> > the primary (e.g. 'itemtype') typing syntax. Schema.org tools may have
> > only weaker understanding of extra types, in particular those defined
> > externally."
> >
>
> I think this is OK but we need to be explicit that for this to work the
> primary type (itemtype) needs to be a part of schema.org or the
> additionalType predicate needs to be fully qualified.
>
I'd like to see some markup example of what this discussion would lead to.
Is there a page in the wiki? In particular, the "primary" vocabulary
defined via @itemtype seems important. I agree with Alexander, looks like
it might be better to recommend schema.org as primary vocab to avoid
confusion.

Other gotchas to be noted for microdata authors:
- if properties of the external vocabulary need to be used, they need to be
full URIs.
- unlike the itemtype attribute which can contain multiple types, only one
type can be defined at a time in each additionalType element. When
specifying multiple additionalTypes for a data item, add an element for
each additional type, e.g.
      <meta itemprop="additionalType" content="
http://purl.org/goodrelations/v1#additionalType1"/>
      <meta itemprop="additionalType" content="
http://purl.org/goodrelations/v1#additionalType2"/>


Steph.