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The Library of Congress > Cataloging Distribution Service > MARC Documentation > MARC 21 Format for Classification Data
MARC 21 Format for Classification Data: Including Guidelines for Content Designation
Network Development and MARC Standards Office, Library of Congress
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Format specifications for the communication of MARC classification records, which may be used in online public catalog retrieval systems, in systems to maintain and develop classification schedules, and in online systems for library classifiers. Defines the codes and conventions (tags, indicators, subfield codes, and coded values) that identify the data elements in the records.

Developed with a focus on two major classification schemes: Library of Congress Classification and Dewey Decimal Classification, but also supports other classification schemes. Includes a glossary of classification terms and full record examples of LC Classification, Dewey Decimal Classification, National Library of Medicine Classification, and Universal Decimal Classification schemes.
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Introduction to MARC Documentation

Machine-Readable Cataloging (MARC) is the standard in library automation. Available in Cataloger's Desktop (

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