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Shared Properties

From: Jeni Tennison <jeni@jenitennison.com>
Date: Sun, 2 Oct 2011 12:20:17 +0100
Message-Id: <FE30E3A1-FC02-4D8C-91E9-5529625ED940@jenitennison.com>
To: public-html-data-tf@w3.org

Pages that contain information about several entities often include common headers or footers that indicated a shared property for those entities. There is an example at the bottom of the section on Associating names with items in the microdata spec [1], where multiple images share a license. Toby Inkster raises the examples of Wikipedia disambiguation pages or tables with groupings [2].

These use cases aren't particularly strong. Hixie has indicated [3] that the support for this in microdata, using itemref, was a side-effect of needing to support microdata fragments that are split across the page rather than due to a specific use case.

Does anyone have any good real-world use cases from their own experience for shared properties? Would anyone volunteer to go looking for pages where the workaround (repeating properties within each entity) would be onerous?


# Microformats #

Microformats don't seem to have any support for shared properties; it looks as if users have to use hidden elements (empty spans) to add the shared properties within the wrapper element for each entity.

# RDFa #

RDFa doesn't have support for shared properties. The RDFWAWG ISSUE-105 [4] is about introducing such a mechanism, but Manu's draft response [5] indicates that it won't happen -- there are technical and backwards compatibility implications for RDFa processors -- unless there's a really good use case.

# Microdata #

Microdata's itemref attribute [6] enables it to support multiple items with shared properties.


If you have pages containing multiple entities which share properties described elsewhere in the page, use microdata.

[1]: http://dev.w3.org/html5/md/#associating-names-with-items
[2]: http://lists.w3.org/Archives/Public/public-rdfa-wg/2011Sep/0083.html
[3]: https://plus.google.com/112095156983892490612/posts/NoCwrzYSHKP
[4]: http://www.w3.org/2010/02/rdfa/track/issues/105
[5]: http://lists.w3.org/Archives/Public/public-rdfa-wg/2011Sep/0066.html
[6]: http://dev.w3.org/html5/md/#attr-itemref
Jeni Tennison
Received on Sunday, 2 October 2011 11:20:55 UTC

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