Using Dublin Core - Appendix, Roles
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|This document describes the use of a subset of the MARC Relator list as a source of role properties for Qualified Dublin Core™.
6. Using Agent Roles in Dublin Core™
MARC Relator terms are properties used to describe the relationship of an agent to a resource by specifying the particular nature of the relationship. They can be used to describe the various roles people and organizations play in the development and use of a resource. The property "Illustrator", for example, can be used for an agent which provided illustrations for the resource.
In Dublin Core, agent roles are expressed as properties (i.e., elements or element refinements). As explained below, most are refinements of the element dc:contributor. In order to identify a subset of MARC Relator Terms as refinements of dc:contributor, DCMI and the Library of Congress cooperated on the evaluation of all (circa) 150 MARC Relator Terms with regard to whether they represented "an entity responsible for making contributions to the content of the resource."
The MARC Relator List: What It Is and How It's Structured
The MARC Code List for Relators was developed for use in MARC 21 bibliographic records to express the relationship between a name and a work. The list includes both role terms and three-character codes representing those terms. The terms were only included on the list when the name and its associated role were considered important enough to include on a bibliographic record as an access point. The Library of Congress is the maintenance agency for this list and regularly adds new terms when a need is expressed and documented. The agreement between DCMI and the Library of Congress specifies that new terms submitted to LC will be referred to the DCMI Usage Board for endorsement of sub-property relationships asserted with regard to Dublin Core™ elements. This agreement is described in the Web document "MARC Relator Terms and Dublin Core™".
The MARC Relator list includes three-character alphabetic codes to be used to identify roles. In addition the list provides definitions for the terms (and associated codes). In MARC records, the codes are synonyms for the term they represent. In DC metadata descriptions, properties are referred to using unique identifiers (URIs), and the codes were used to form unique identifiers for these properties. The list of MARC Relator Terms is maintained by the Library of Congress, so the terms have been assigned URIs on the basis of a namespace established by LC. Schemas or instance metadata will need to cite these URIs (or the MARC relator namespace) in order to use any of the MARC Relator properties, be they sub-properties of Dublin Core™ elements or not. See the document "Guidelines for Implementing Dublin Core™ in XML" for specific information on using non-DCMI namespaces.
In addition to providing Web documentation of the MARC Relator Terms, the Library of Congress provides a representation of the MARC Relator Terms in RDF/XML. Refinements of dc:contributor are, in the RDF/XML representation, asserted to be sub-properties of dc:contributor. In RDF/XML, this is done as follows:
<rdf:Description rdf:about="http://www.loc.gov/loc.terms/relators/ILL"> <rdfs:subPropertyOf rdf:resource="http://purl.org/dc/elements/1.1/contributor" /> </rdf:Description>
In determining whether a sub-property relationship was to be asserted, LC and the Usage Board took a fairly narrow view. The relationship was asserted only if the contribution was judged to apply, by its nature, to the content of the resource. For example, whether or not "binder" is to be considered a sub-property of dc:contributor depends on the nature of the resource. Where the resource in question is valued as an art object, a binder may be construed as a "contributor" to its content; in other cases, the binder may not have this role.
Roles as refinements of Dublin Core™ elements
A subset of MARC Relator Terms have been identified as refinements of dc:contributor. The MARC Relator term marcrel:CRE (Creator) is asserted to be a sub-property of both dc:creator and dc:contributor. In a few cases, MARC Relator terms are considered to be refinements of Dublin Core™ elements other than dc:contributor. The MARC Relator terms marcrel:PBL (Publisher) and marcrel:DST (Distributor) are considered refinements of dc:publisher, as a publisher may or may not also be a "contributor" to the resource. The term marcrel:DPC (Depicted) is considered a sub-property of dc:subject.
Because roles are generally used with dc:contributor, appropriate "Dumb Down" of most agent refinements in the MARC Relator subset will be to dc:contributor, with exceptions noted above. Implementors may choose to describe "creators" using either marcrel:CRE (which will dumb down both to dc:creator and dc:contributor) or dc:creator (which will remain distinct from dc:contributor in Simple Dublin Core).
A document with further examples of refinement relationships and Dumb Down, along with examples of usage in XML, XHTML and RDF/XML, can be found at: http://www.ukoln.ac.uk/metadata/dcmi/marcrel-ex/.
Terms Not on the MARC Relators List
The MARC Relator list has been developed over many years to meet a wide variety of needs. New terms are added on the basis of need, and LC has expressed willingness to continue to expand the list upon request. Implementers also have the option to create and expose alternative vocabularies for the expression of other kinds of roles not reflected in the MARC Relator list.
For those implementations wishing to use terms from the MARC relators list that do not have a sub-property relationship to Dublin Core™ elements, it should be noted that an implementation may use such terms with no intrinsic harm to interoperability by using them directly, as elements, in their metadata. In the context of a Dublin Core™ record based on an application profile using MARC relator terms, roles not on the list as valid sub-properties endorsed by DCMI could be used in a Qualified DC expression, but not in a Simple DC expression.
Managing the Use of Role in an Implementation
The full MARC Relator list includes approximately 150 separate terms for various roles. A subset includes sub-property relationships with DC elements endorsed by DCMI. Even within this subset some of the relator terms on the list were created for specific domains and would be of little use in other communities. It might therefore be useful for implementations to declare a further subset of the relator vocabulary as relevant to their specific goals, preferably by way of a formal application profile.
The full list of MARC Relator Terms (including refinements of Dublin Core™ elements): http://www.loc.gov/loc.terms/relators/
The subset of MARC Relator Terms which refine Dublin Core™ terms: http://www.loc.gov/loc.terms/relators/dc-contributor.html
The RDF representation of MARC Relator Terms: http://www.loc.gov/loc.terms/relators/dc-relators.xml
For further information, see "MARC Relator Terms and Dublin Core™" http://dublincore.org/usage/documents/relators/.
2005-01-16, Errata: broken link repaired.