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History of the OCLC number


This appendix describes briefly the various forms of OCLC numbers that OCLC has output in OCLC-MARC via subscription and export from various OCLC cataloging services.

OCLC has distributed other records with different kinds of control numbers. The records below are not part of this appendix because they are not WorldCat records.

code record type
oca OCLC-MARC authority records
bip (obsolete) Book-in-Print database records
ccd (obsolete) CatCD original record (both bibliographic and authority)
har (obsolete) Harvard database record
pct PromptCat data record
pks (obsolete) Prism Keying Service record

Records output prior to June 28, 1981

Prior to June 28, 1981, the OCLC number was distributed in field 001 with the following structure:

tag byte value definition
001     Control Number (NR)
  00-03 ocl7 OCLC identifier
  11   Blank


001 ocl70012345

Note: transaction date

Between June 30, 1980 and June 25, 1983, all output records included the transaction date following the control number in field 001, separated by a blank. Beginning June 26, 1983, the transaction date was moved to field 005 and no longer put in field 001.


001 2345 800630

Records output between June 28, 1981 and the 100 millionth record in WorldCat

Includes all records output regardless of when the library updated or added the record. Records produced prior to June 28, 1981 but output after that date have the new structure:

tag byte value definition
001     Control Number (NR)
  00-02 ocm OCLC identifier
  11   Blank

 Note: See Note: transaction date above.

date example field
Prior to June 28, 1981 001 ocm0012345 800630
After June 28, 1981 001 ocm0012345

Records output after the 100 millionth record in WorldCat

If the OCLC number is greater than 100000000, the following structure will be present:

tag byte value definition
001     Control Number (NR)
  00-02 ocn OCLC identifier


001 ocn198765401

Cross-reference field

Beginning in December 1979, for every record that is merged to another record, a field 019 (OCLC control number cross-reference) is created. It is added to the retained record and contains the OCLC number of the deleted record. For more information, see Bibliographic Formats and Standards, field 019.


001 ‡a9849497‡a10625879


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