Posted at http://lists.w3.org/Archives/Public/public-html/2010May/0253.html:

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Date: Sat, 15 May 2010 06:42:52 -0400
From: Thomas Baker <[log in to unmask]>
To: HTML working Group <[log in to unmask]>
Subject: Comments on HTML5 proposals from the DCMI community

Comments on HTML5 proposals from the DCMI community

DCMI is interested in promoting any generic, standards-based
solutions which ensure that its properties are precisely
identified and can be referenced and used without ambiguity.

To date, the Dublin Core community's use of data in X/HTML has
focused on the case of "document metadata", data "about" the
document itself, expressed as RDF triples encoded using the
<meta> and <link> elements, using an HTML meta data profile
known as "DC-HTML" (reference), which is associated with a
GRDDL Profile Transformation.

While this work is based on the profile mechanism and on
GRDDL, DCMI does not consider itself to be constrained to
those approaches if alternative approaches in HTML5 meet the
requirements of the DCMI community.

DCMI also recognises the value of being able to encode RDF
data in the body of an X/HTML document, data either "about"
the document or about other resources, and of the use of a
common syntax for data in the head and the body.

For document metadata in HTML5, the principal need of the
Dublin Core community is for a mechanism to encode RDF triples
using <meta> and <link> elements which:

-- supports both literal and URI objects
-- supports the intermixing of any independently created property 
   URIs, not just property URIs owned by DCMI
-- includes an abbreviation mechanism for property URIs, not just 
   for property URIs owned by DCMI, but for property URIs generally.

RDFa provides a mechanism for encoding document metadata that
meets these requirements, as well as for encoding data about
any resources in the body of the document. RDFa supports the
abbreviation of URIs using CURIEs -- i.e., RDFa would meet
DCMI's requirements for metadata in HTML5, and DCMI would be 
happy to promote the use of RDFa in HTML5 in place of the current
DC-HTML profile.

If the new microdata proposal were to provide a mechanism for
achieving the same effect, then DCMI would be happy to promote
its use as well.  Based on an imperfect understanding of the
proposal on the table, DCMI does have some concern that
requiring the use of full URIs for qualifying the provenance of
properties sets a high bar for implementers, who could resort to
pragmatic solutions that would depend on out-of-band information
or other forms of "context" to relate the properties used
specifically to DCMI metadata terms and could therefore, in
practice, introduce ambiguity about the precise terms referenced.

In this sense, Microdata as currently proposed does not meet
DCMI's requirements for metadata in HTML5.  If the @profile
attribute were removed from HTML5 and RDFa were also not
available in HTML5, this would leave no mechanism which meets
the requirements outlined above.

Background

Over the years, DCMI has developed several specifications
of relevance to the discussions around HTML5:
--  RFC 2731 of 1999 ("Encoding Dublin Core Metadata in HTML") [1],
    now obsoleted by RFC 5791 ("RFC 2731 Is Obsolete") of 2010 [2].
--  "Expressing Dublin Core in HTML/XHTML meta and link elements" of 2003 [3],
    currently a "superseded recommended" as explained in [4].
--  "Expressing Dublin Core metadata using HTML/XHTML meta and link
    elements" (a.k.a. DC-HTML) of 2008 [5], currently a DCMI Recommendation.

The 2008 DC-HTML Recommendation makes use of the XHTML meta data
profile, which is associated with a Profile Transformation as
defined by GRDDL.

DCMI acknowledges that all technology is transitional, and that,
in particular, syntax for embedding metadata in HTML is likely
to evolve significantly over the next few years.

The intention of DCMI is to help metadata implementers use
metadata effectively in the Web environment.  While
DCMI-specific solutions have been developed over the years to
meet pressing needs, DCMI's intention is not to promote
syntactic solutions that are specific to "Dublin Core", but
rather to enable the use of Dublin Core terms in metadata that
draws on other compatible namespaces, such as FOAF, in the
context of application profiles.

Increasingly, such syntax solutions are being developed outside
of DCMI. Since the finalization of RDFa as a W3C Recommendation
in 2008, DCMI also promotes RDFa for use in "Dublin Core"
metadata as an alternative to DC-HTML/2008.

In this spirit, DCMI does not consider itself to be committed
to the profile attribute in a way that would preclude migration
to alternative mechanisms in HTML5.  DCMI is open to any forms of
markup that will meet the needs of the Dublin Core community.

Best regards,

Tom Baker (CIO of DCMI), Pete Johnston, Mikael Nilsson, Andy Powell
on behalf of DCMI

[1] http://tools.ietf.org/html/rfc2731
[2] http://tools.ietf.org/html/rfc5791
[3] http://dublincore.org/documents/dcq-html/
[4] http://dublincore.org/documents/dc-html-notes/
[5] http://dublincore.org/documents/dc-html/


-- 
Thomas Baker <[log in to unmask]>