OCLC Number Prefixes Overview

This page gives an overview of what OCLC prefixes are and why they should not be included in records with OCLC numbers contributed to the Central Catalog.

What is an OCLC prefix?

Every OCLC control number (OCLC number) has a prefix of two or three letters. This prefix, called an "OCLC identifier", distinguishes a record that originated in the OCLC system.

on1257403412   ocn910622914   ocm56316360

The original prefix was "ocm", but as the number of records increased in WorldCat over the years, OCLC changed the prefixes to include "ocn" and "on" to allow for longer OCLC numbers. This ensures the ever-growing number of records have unique numbers upon creation in OCLC's WorldCat. More information about the history of OCLC number prefixes are available at OCLC's website.

What happens to these prefixes when I load records from OCLC into my local catalog?

It depends on how your local loader is set up. The loader can do one of two things: keep the 001 prefix or remove it. If kept, the OCLC prefix remains in the 001 field as part of the OCLC number.

Many loaders are set up to remove alpha prefixes (prefixes starting with letters) before the number and will only keep the numeral portion. Loaders can also be changed, so it's possible that an older version of a loader kept 001s with the prefix, but the current loader does not. This can result in a local catalog in which older records include OCLC prefixes in the 001 while more recently loaded records do not.

How does the OhioLINK Central Catalog handle control numbers?

The OhioLINK Central Catalog (Central) uses the 001 record control number field as its initial match point. Records sent to Central are assumed to be contributed without prefixes. Since the record numbers are usually OCLC numbers, they are matched and local records for the same content merge into a single record in Central that lists all contributing members' holdings.

Records with non-OCLC 001s that are contributed to Central have a special formula to keep their vendor prefix. One example is the Safari colleciton in which "1safari" is used before the record number. The loader keeps this prefix because it begins with a number, which allows this collection of vendor records (without OCLC numbers) to be maintained separately.

When records with OCLC prefixes are contributed to Central, the prefix prevents a match with the same OCLC record that doesn't have the prefix.

ocm56316360 will not match with 56316360

The above example creates a duplicate record in Central instead of adding all local holdings to the same record. This is why all records with OCLC numbers contributed to Central should not include OCLC prefixes.

OCLC prefixes (on, ocn, and ocm) should be removed from the 001 in local records that are contributed to Central.

Created February 2022