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.