RDA Toolkit has always offered an alignment between RDA elements and the MARC 21 Authority and Bibliographic formats. This is not, strictly speaking, a linked data or semantic map because there is no formal representation of MARC 21 in Resource Description Framework (RDF). Instead, an alignment matches an RDA element to a string that represents the corresponding MARC 21 tag, indicators, and subfield. The alignments are one-to-many: a single RDA element aligns with multiple combinations of tag, indicators, and subfield. The alignments are complex.
The 3R Project has restructured the alignments in the Toolkit from a separate table to presentation in context, within the Element reference section of the relevant RDA element. The Element reference section also contains semantic mappings to Dublin Core Terms and the IFLA Library Reference Model's entity-relationship formulation, and there are plans to add mappings to BIBFRAME and UNIMARC in due course.
One of the goals of the 3R Project was to improve the context of guidance and instructions in RDA Toolkit. As a result, the tables in the original Toolkit that provided alignments between RDA elements and MARC 21 encoding formats for Authority and Bibliographic records have been moved to the RDA Registry.
The tables have been replaced by spreadsheets which are used to manage the content of the Element reference sections in the new Toolkit. The alignments are presented in the context of a specific element, and the separation from guidance and instructions is minimized while remaining distinct.
The sets of alignments for each MARC 21 format are now available for download from the RDA Registry. The downloads are in comma-separated variable (csv) format which can be easily imported into spreadsheet software for display and local processing.
Local processing includes sorting the alignments by encoding string to display the inverse alignments to RDA elements, and filtering to restrict the display to specific recording methods.
The unique label of an RDA element can be matched to other RDA Registry downloads for the RDA element sets, to allow the encoding strings to be included in a local application profile.
The alignments are a work in progress that is carried out by the British Library (for MARC 21 Bibliographic) and Libraries and Archives Canada / Bibliothèque et Archives Canada (for MARC 21 Authority). An outcome of the October 2020 meeting of RSC is the formalization of this activity as the RDA/MARC 21 Alignment Task Force, reporting to the RSC Technical Working Group.
MARC 21 Authority format
Landing page: http://www.rdaregistry.info/Aligns/alignRDA2M21A.html
MARC 21 Bibliographic format
Landing page: http://www.rdaregistry.info/Aligns/alignRDA2M21B.html
Machine-readable maps based on the alignments are also available for download.
All RDA alignments, maps, and element sets are included in the latest GitHub release of RDA Vocabularies, available as a single compressed download.
RDA Vocabularies v4.0.1 (https://github.com/RDARegistry/RDA-Vocabularies/releases/tag/v.4.0.1)
5124 alignments for Authority format
16857 alignments for Bibliographic format