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Re: Updated Microdata to RDF Working Draft

From: Adrian Giurca <giurca@tu-cottbus.de>
Date: Wed, 26 Sep 2012 15:28:35 +0200
Message-ID: <50630303.3000903@tu-cottbus.de>
To: Gregg Kellogg <gregg@greggkellogg.net>
CC: Semantic Web <semantic-web@w3.org>, "public-html-data-tf@w3.org WG" <public-html-data-tf@w3.org>, "public-vocabs@w3.org Vocabularies" <public-vocabs@w3.org>
Hi Gregg and all,

A large work on Vocabulary Expansion described in Section 4 of the 
working draft work [1] is based on some constraints of the Microdata 
specification [7 <#7>]:

/Microdata requires that all values of @itemtype come from the same 
vocabulary. This is required as @itemprop values are resolved relative 
to that vocabulary/

I slightly changed your Example 13 from [1]  to allow two types and two 
properties:

<div itemscope itemtype="http://schema.org/Person">
   <link itemprop="additionalType" href="http://xmlns.com/foaf/0.1/Person" />
   <p itemprop="|email|">mail@gmail.com</p>
</div>	

I would like to use foaf:mbox on the above example and it seems to me 
that following the current spec [7] is difficult if not impossible. 
Possible solutions such as:

<meta content="mailto:mail@gmail.com" itemprop="http://xmlns.com/foaf/0.1/mbox"/>

may don't work as a processor may relate http://xmlns.com/foaf/0.1/mbox 
to http://schema.org/Person and not to the "additional type".

  (the original example with GoodRelations was somehow different as any 
GoodRelation Product is subclass of http://schema.org/Product therefore 
the @name property is  inherited by Goodrelations Product)

I kindly ask you, also people from the HTML data task force as well as 
Microdata spec editors about *rationales behind the actual Microdata 
specification* [7 <#7>] . I understand the concern of using namespaces 
but still is not enough clear why @itemtype and @itemprop does not allow 
items from different vocabularies.

Indeed, allowing multiple vocabularies  using only @itemtype and 
@itemprop attributes and no namespaces requires processors to relate to 
schemas of these vocabularies and may also introduce name ambiguity (as 
schema does not provide URI for properties).

In any case adding @additionalType may not be the most elegant solution 
as it appears  not solving the problem of multiple vocabularies.

Thank you,
Adrian Giurca

[7] 
http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html

On 9/20/2012 8:22 AM, Gregg Kellogg wrote:
> I've prepared an updated Microdata to RDF Working Draft for review [1]. Please note that, as this is a Note of the Semantic Web Interest Group, and the HTML Data Task Force is complete, the official place for feedback is semantic-web@w3.org.
>
> This update adds support for vocabulary expansion, principally to support features such as schema:additionalType. Microdata vocabulary expansion is a subset of RDFa vocabulary expansion, and is fully compatible with RDFa, such that toolsets which process both RDFa 1.1 and Microdata to RDF can use a single vocabulary expansion algorithm, although its use in Microdata is mandatory, whereas it is optional in RDFa 1.1.
>
> To support vocabulary expansion, additional features are added to the registry: within a vocabulary, a property can be either specified as "equivalentProperty" of another IRI, or "subPropertyOf" another IRI, to use either owl:equivalentProperty or rdfs:subPropertyOf expansion rules. The default registry has been updated for additionalType as follows:
>
> {
>    "http://schema.org/": {
>      ...
>      "properties": {
>        "additionalType": {"subPropertyOf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#type"}
>        ...
>      }
> }
>
> Note that the current published registry [2] has not been updated. The version of the registry used for this working draft is available in the supplement [3], and in the mercurial repository [4].
>
> Additionally, when a vocabulary is detected, an rdfa:usesVocabulary triple is generated, which enables the RDFa 1.1 vocabulary expansion toolchain. If at some point schema.org includes OWL2 expansion rules supported by RDFa within the vocabulary definition, this will allow full use of this through RDFa tool chains which support Microdata to RDF.
>
> The draft references the test-suite [5], which now has a number of tests (currently 74) available to help developers check processor conformance. This includes all of the current schema.org microdata examples.
>
> After a reasonable feedback period, this working draft will update the current published note [6].
>
> Thanks to Ivan for invaluable help in preparing this update.
>
> Gregg Kellogg
> gregg@greggkellogg.net
>
> [1] http://dvcs.w3.org/hg/htmldata/raw-file/default/ED/microdata-rdf/20120919/
> [2] http://www.w3.org/ns/md
> [3] https://dvcs.w3.org/hg/htmldata/raw-file/default/microdata-supplement/index.html
> [4] https://dvcs.w3.org/hg/htmldata/raw-file/default/microdata-namespace/ns.json
> [5] http://dvcs.w3.org/hg/htmldata/raw-file/default/microdata-rdf/tests/
> [6] http://www.w3.org/TR/2012/NOTE-microdata-rdf-20120308/
>
Received on Wednesday, 26 September 2012 13:29:30 GMT

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