In March 2006, the DCMI Directorate awarded a contract to Mikael Nilsson
(Royal Institute of Technology, Sweden) to draft a revision of
the existing specification for expressing Dublin Core in RDF.
The result of this work is a new working draft titled "Expressing Dublin
Core metadata using the Resource Description Format (RDF)"
http://dublincore.org/documents/2006/05/29/dc-rdf/
which will be available for comment by 17:00 EST on Tuesday, 30 May.
As described in DCMI's "Procedure for approval of DCMI metadata terms
and recommendations" [1], proposals subject to Public Comment are
announced on DC-GENERAL and posted on the DCMI Web site for a period of
at least four weeks. During that time, any interested member of the
public may submit a comment, either publicly to a DCMI mailing list such
as DC-ARCHITECTURE, non-publicly through DCMI Feedback
([log in to unmask]), or directly to the issuer of the
announcement.
About the document
==================
This document provides draft recommendations for expressing DC metadata
using RDF, the Resource Description Framework. It does this by
describing how the features of the DCMI Abstract Model [2] are
represented using the RDF model.
Subject to public review and discussion in the context of DCMI process,
the May 2006 Working Draft is intended eventually to replace two legacy
DCMI documents:
* Expressing Simple Dublin Core in RDF/XML [3], a DCMI Recommendation
from July 2002;
* Expressing Qualified Dublin Core in RDF / XML [4], a DCMI
Proposed Recommendation from May 2002.
The document "Notes on DCMI specifications for Dublin Core metadata in
RDF" [5] describes in more detail how this draft relates to the earlier
specifications. DCMI is seeking comments from affected communities, and
the content of any new DCMI Recommendation will depend on feedback
received from these communities.
The motivation for the new Working Draft was to provide an RDF
expression that
* provides a unified specification for Dublin Core in RDF
* provides full support for the DCMI Abstract Model
* provides good integration with other RDF metadata
The Working Draft is based thoroughly on the DCMI Abstract Model,
and includes a number of important changes to the previous
specifications, such as:
* Support for domains and ranges of properties
* Support for multiple value string for a single value
* Support for RDF datatypes
* Deprecation of rdf:value (introduction of dcrdf:valueString)
* Deprecation of RDF Containers
* Deprecation of "poor man's language qualification"
* Deprecation of "poor man's structured values"
All of the above are issues that we hope to get feedback on during the
public comment period.
Support for domains and ranges
==============================
The most significant change introduced by the May 2006 Working Draft is
the addition of support for domains and ranges of properties in general,
and of DCMI-defined properties in particular.
The two legacy RDF expressions differ with regard to whether properties
such as dc:creator and dc:date have values that are non-literal
resources (e.g., a Person or a Date, seen as entities), or strings
representing the resources (i.e., a value string).
As part of the process of clarifying the RDF expression for Dublin Core
metadata, it has become evident that DCMI would benefit from
supplementing its English-language definitions with
machine-understandable declarations of domains and ranges. As of the
time of writing, the DCMI Usage Board is considering the assignment of
formal domains and ranges which make explicit the meanings intended in
the current natural-language definitions [6].
In accordance with the current approach, the DCMI Usage Board is
considering the assignment of a range of "Agent" to dc:creator and
dc:contributor, where "Agent" would be defined as "the class of all
things that are a Person, Organization, or Service". Similarly,
appropriate ranges would be specified for the other DCMI terms as well.
Legacy RDF metadata
===================
The assignment of any specific range would make one or another part of
the legacy metadata appear invalid in the context of machine processing.
Declaring "Agent" as the range of dc:creator would mean that inferencing
applications would expect to treat the value of the dc:creator property
as a non-literal entity.
The legacy specifications did not properly address these ambiguities,
with the result that an unknown amount of Dublin Core-based RDF data is
inconsistent with the definitions of the Dublin Core properties.
The new Working Draft is an attempt at providing a long-term solution to
this issue, but as this has important consequences for the processing of
legacy Dublin Core metadata in RDF, we hope that the affected
communities will forward their comments on this matter.
The Notes [5] provides more details on the matter.
/Mikael
[1] http://dublincore.org/usage/documents/approval/
[2] http://dublincore.org/documents/abstract-model/
[3] http://dublincore.org/documents/dcmes-xml/
[4] http://dublincore.org/documents/dcq-rdf-xml/
[5] http://dublincore.org/documents/2006/05/29/dc-rdf-notes/
[6] http://dublincore.org/usageboardwiki/PropertyDomainsAndRanges
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