The Library of Congress Network Development and MARC Standards Office announces completion of a schema for MARC 21 records in an XML structure for use in communicating MARC 21 records. It is available from http://www.loc.gov/marcxml. This schema was developed in collaboration with OCLC and RLG and reviewed by the National Library of Canada and the National Library of Medicine (NLM), after a survey of schemas in use in various projects. Many schemas have taken the "slim" approach but all vary slightly. This schema will be maintained by the Library of Congress as will software that enables lossless conversion to and from MARC 21 records in the ISO 2709 structure. As illustrated in the introductory information on the web site, the Library of Congress will develop and provide, downloadable from the MARCXML web site, tools for various transformations and for record validations. A single schema serves all the five MARC 21 formats.
By collaboratively developing a communications schema, the Library of Congress encourages the standardization of MARC 21 exchange records in the XML environment, recognizing that MARC 21 records inside systems will continue to use different record configurations, tailored to the characteristics of the system. Provision of the tools for transformations to and from other metadata approaches, such as Dublin Core and the Metadata Object Description Schema (MODS), will help to standardize derivative metadata records also. (MODS is a new schema for a bibliographic element set that is a subset of MARC expressed in XML with language-based rather than numeric tags.) The tools take the mappings between MARC and other metadata sets, that have been maintained on the MARC web site, to an operational level.
One project interested in a standard, lossless MARCXML schema is the Open Archive Initiative (OAI) which found it necessary to draft a schema in the absence of an official one. The Library of Congress worked with the OAI to provide a transformation from the original oai_marc schema to this one so the Initiative can take advantage of a schema that is maintained by the MARC 21 maintenance agency and in broad use. The transformation is available from the MARCXML web site.
With the slim approach, schema-driven validation is only possible at the highest structural level. The Network Development and MARC Standards Office will therefore maintain downloadable tag, subfield, and value validation software on the web site that will enable users to build validation programs for their needs. Use of these standard validations represent another attempt to assure standardization of records to support effective record interchange.
The Library has maintained two SGML DTDs (for Bibliographic-type and Authority-type records) since 1996, which take a different approach to the data elements in MARC B an approach that enables validation of data through the DTD itself but requires a very large DTD and DTD maintenance. The Bibliographic-type DTD was converted to an XML DTD in 2000. These DTDs have been effectively used by some agencies (including the Library of Congress), primarily for internal processes, therefore transformations between them and the new slim MARCXML schema are being provided. Maintenance techniques and/or possible revision of the XML DTDs are under consideration.