Squaring the new RDA standard with the Machine-Readable Cataloging (MARC) encoding format is a source of much concern and confusion. RDA is not an encoding standard; it is a content standard. It makes no mention of MARC, nor did the creators of RDA have MARC “in mind” when they drew up RDA. Clearly put, RDA says a lot about what information to record, a little about how to record it, and nothing at all about where it goes or how to encode it. One problem created by this situation is that a typical MARC bibliographic record is a “mash-up” of FRBR group 1 entities (i.e., WEMI). It may contain in its fields data referring to the work, expression, manifestation and item of a particular resource. The powerpoints “MARC 21, FRBR, RDA,” prepared by the LC, and “MARC 21, RDA, and the FRBR and FRAD models,” prepared by OCLC, both noted in the resources section of this document, are good sources of information on how RDA maps into MARC.
Despite these resources, it is not always easy or straightforward to map RDA instructions to MARC fields. Consider a standard MARC bibliographic record. Some fields, such as 260—publication information—and 300—physical description—clearly refer to the manifestation of a work (as does the title proper in the 245 field). The creator in the 100 field is in relationship to the work, but a translator or illustrator listed in field 700 would be related to an expression. In the same way, the uniform title (now “preferred title”) in the 240 field is the work, but the language—the $l subfield of the 240 field—points to an expression. Understanding these distinctions can help you clarify the practical side of RDA’s theoretical foundation and also point you toward the relevant section of the RDA instructions.
In a fully RDA-compliant catalog, it is possible that there would be individual “records” for expressions and (more likely) works, thus separating the “mashed-up” information now in the standard bibliographic record. It remains to be seen whether these sorts of separate records will ever be widely adopted in MARC. For the moment, the RDA entities will be all mixed in the bibliographic and authority records of a standard catalog. The long-term future of MARC is (and has been for a long time) up in the air, but the reality is that we will be using MARC for some time to come, and RDA will have to work within it.