Data sync uses OCLC control numbers in your records in the following ways:
- Match WorldCat records
- Link local records from local systems to WorldCat records
Because the format of OCLC control numbers has changed over many years and many local systems remove it or put it in a field other than 035, OCLC batch services uses preprocessing routines to map existing OCLC control numbers to field 035 $a, prefixed with (OCoLC).
The following table describes the changes in OCLC control numbers formatting and location over time. Records can contain any of these formats and locations for the OCLC number.
|In records created 12 November 2006 and before, field 001 contains the OCLC control number ocm.||
OCLC numbers 1 through 99999999:
|In records created after 12 November 2006, field 035 contains the OCLC control number ocn.||
OCLC numbers 100,000,000 and higher:
|Sometime after November 2006, the OCLC control number in field 035 ‡a is prefixed by (OCoLC).||OCLC number is a variable-length numeric string with no leading zeros.||(OCoLC)198765401|
Field 019 contains the OCLC control number of a deleted or merged record replaced by the current one.