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Re: Multiple itemtypes in microdata

From: Gregg Kellogg <gregg@kellogg-assoc.com>
Date: Tue, 18 Oct 2011 16:24:27 -0400
To: Ian Hickson <ian@hixie.ch>
CC: Bradley Allen <bradley.p.allen@gmail.com>, Stéphane Corlosquet <scorlosquet@gmail.com>, "public-html-data-tf@w3.org" <public-html-data-tf@w3.org>
Message-ID: <A24DD4AE-BCC5-46F5-B048-80FD6D94A08D@greggkellogg.net>
On Oct 13, 2011, at 8:48 PM, Ian Hickson wrote:

...
Incidentally, note that you can't just take, say, an RDF vocabulary, or a
Microformats vocabulary, and just use it in microdata directly. A
microdata vocabulary has to define processing rules that are often not
provided for RDF and Microformats vocabularies, and has to use the terms
defined in the HTML specification to describe how the terms work. You can
see examples of how to define vocabularies in the HTML standard:

  http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#mdvocabs

Hixie, note that I raised property URI generation as ISSUE-1 [1] (along with other transformation issues). From reading the HTML/Microdata spec, it would seem that processors really need to have vocabulary-specific rules for interpreting these rules. This is important for property URI generation, but also for maintaining value order and specifying per-property literal datatypes.

The alternatives are:

1) bake in support for each vocabulary into a conformant processor
2) read a vocabulary document (i.e., RDFS or OWL) and determine processing rules from rdfs:range/rdfs:domain specifications
3) do nothing, use a single processing algorithm that is generic across all vocabularies and leave it to post-processing to perform vocabulary-specific modifications. (Although this does not really address property URI generation variation between vocabularies defined in HTML and other RDF vocabularies).

Note, that if the HTML spec specified http://microformats.org/profile/hcard# as the vCard type, instead of just http://microformats.org/profile/hcard, properties would be generated relative to the type using processing rules currently described in [2], which is intended to be compatible with schema.org<http://schema.org> and other RDF vocabularies.

Gregg

[1] http://www.w3.org/2011/htmldata/track/issues/1
[2]  https://dvcs.w3.org/hg/htmldata/raw-file/24af1cde0da1/microdata-rdf/index.html

HTH,
--
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Tuesday, 18 October 2011 20:25:27 GMT

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