Guidelines for using Agent Roles in Dublin Core (Draft) An Appendix to: "Using Dublin Core" 1/23/04, dih 2/12/04, rsg 2/16/04, dih 9/2/04, dih 9/29/04, rsg 9/30/04, dih 5/9/05. dih 5/11/05 rsg I1. Background The need to express a role for the "Agent" elements (Creator, Contributor, and, to a lesser extent, Publisher) in the Dublin Core element Set has been expressed for many years and there have been a number of ideas proposed for how to accommodate this need. A role is a term that further refines the contribution of the agent to the resource described by specifying the particular contribution. An example is that "illustrator" might be a role associated with the element Contributor when that person provided illustrations to the resource rather than being responsible for other aspects of the intellectual content. The DCMI Usage Board has discussed the issue several times and agreed that the role values are properly element refinements. At its meeting in Florence in Oct. 2002, the Board considered deprecating Creator and Publisher in favor of Contributor, since the role values Creator and Publisher could be used to refine Contributor if needed. Because of negative response to this level of change in the Dublin Core element set, the DCMI Usage Board decided to recommend role refinements only to Contributor, but to leave Creator, Contributor and Publisher as separate elements. Because a standardized, widely adopted list of roles already existed in the MARC Code List for Relators, it was recommended early in these discussions that DCMI not develop its own. Although earlier discussions considered defining only a small subset of the list available for use with Agent elements, there was consensus in the DC Libraries Working Group (which was developing an application profile including use of the MARC relator terms) and the Usage Board that users should not be constrained by a restricted list of elements and that the entire list of relator terms should be available given the difficulty of anticipating needs in various domains. In order to be consistent with DCMI principles and practice, relator terms to be used as element refinements must not extend the scope of the semantics of dc:contributor. The UB agreed that, in principle and practice, refinements of elements must in every case be a valid subproperty by refining rather than extending the semantics of that element or property. The obvious solution was to specify which terms are subproperties of dc:contributor by virtue of falling under the definition of "an entity responsible for making contributions to the content of the resource." 2. The MARC Relator list: what it is and how it's structured The MARC Code List for Relators was developed by the Library of Congress 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 that represent those terms. The terms are only included on the list when the name and its associated role are 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 the need is expressed and documented. The MARC Relator list includes three-character alphabetic codes to be used to identify roles. These are to be considered synonyms for the terms they represent. In addition the list provides definitions for use of the term/code. 3. Application Relator terms that are considered to refine the semantics of "an entity responsible for making contributions to the content of the resource", are designated as such by including a statementan assertion that it is a subproperty of dc:contributor. Terms that do not contain this assertion are not to be considered a refinement of dc:contributor. In determining whether the subproperty assertion applies, LC and the Usage Board took a fairly narrow view. The assertion is included only if that contribution always applies in terms of the content of the resource. For example, "binder" does not have the subproperty assertion, since it depends upon what the resource is; sometimes a binder may contribute to the content if the item is valued as an art object, while in other instances, the binder has not contributed to content. The Library of Congress has prepared an RDF expression of the MARC relator list, to be used in conjunction with the Dublin Core element Contributor. The following designates whether the particular role term is a subproperty of dc:contributor as follows: . In the RDF representation, the codes are tokens to be used for the term and are part of the URI. In some cases unused terms refer to used terms; these are included in the RDF representation as a note (dc:description). For those implementations wishing to use terms from the MARC relators list that do not have a subproperty relationship to dc:contributor, an implementation may use these terms with no intrinsic harm to interoperability by using those terms directly as MARC relator terms. As an example: Original term Dumb-down "Simple DC" marcrel:degreeGrantor marcrel:degreeGrantor --- marcrel:owner marcrel:owner --- marcrel:illustrator dc:contributor dc:contributor Thus, in the context of a DC record based on an application profile using MARC relator terms, usage of roles not on the list of valid subproperties approved by DC could be used in a Qualified DC expression, but not in a Simple DC expression, according to the rules for dumb-down. In order to minimize the possibility of confusion, the Usage Board has authorized the use of roles only with the element Contributor. Because Creator is in some sense a role elevated to a position at the level of element, the Board decided that it there is little value in providing another level of roles beneath that particular element. An assertion is made that marcrel:publisher is a subproperty of dc:publisher, because its semantics are narrower; in this instance publisher may or may not also be a contributor to the resource, so the subproperty of contributor assertion is not made. In the case of marcrel:creator, an assertion is made that it is a subproperty of dc:creator, also because of narrower semantics and it is also a subproperty of dc:contributor. If marcrel:creator is used instead of dc:creator, this should be done consistently-- the two terms should probably not be used together in the same instance. In addition, the term "depicted" is asserted as a subproperty of dc:subject and "distributor" a subproperty of dc:publisher. Because roles are to be used only with the Contributor element, appropriate "Dumb Down" of all agent refinements (except "depicted" and "distributor") expressed as roles will be to Contributor. Given this, implementors may choose (preferably within the context of an application profile), to specify explicitly whether the MARC relator term of creator should be used, based on the fact that the distinction could be retained in Simple Dublin Core if the Element level term is retained for those particular roles. Using Roles in XML and other Schemas Because the maintenance of the MARC Relator list will remain with the Library of Congress, the namespace of the roles will be established by LC and will not be a DCMI namespace. Thus, schemas will need to include the MARC relator namespace in order to properly express role terms. See the document Guidelines for Implementing Dublin Core in XML for specific information on using non-DCMI namespaces. 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 will continue to expand the list upon request, and a process to evaluate new terms will be initiated. 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. [d1]. Managing the Use of Role in an Implementation The full MARC Relator list includes approximately 150 separate terms for various roles. LC also provides a list of the subset that may be used with dc:contributor at: http://lcweb2.loc.gov/cocoon/relators/dccontributor.html. Even within this subset some of the roles 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 role vocabulary as relevant to their specific goals, preferably by way of a formal application profile. Additional Information and Examples: A document containing additional technical information about the use of MARC Relator terms as well as examples of usage in XML, XHTML and RDF/XML can be found at: http://www.ukoln.ac.uk/metadata/dcmi/marcrel-ex/ The full MARC Relator list in RDF can be found at: http://lcweb2.loc.gov/cocoon/relators/relators.xml The subset of terms to be used with dc:contributor is at: http://lcweb2.loc.gov/cocoon/relators/dccontributor.html.