Have you ever looked at an OCLC number in your ILS and wondered what those prefixes (all the letters before the number) really mean? Well, I have. It is quite possible that I learned this in Grad. School, but quite frankly that was a long time ago and I don’t remember if that was something we were ever taught.
For most of my time cataloguing, I haven’t really given those prefixes a second thought. Sure, they are there, but they haven’t seemed to matter or affected my ability to find and catalogue the item I have in hand. At least, I have never noticed that they have.
The OCLC number resides in MARC field 001, but is usually put in the 035 field by local ILS systems when exported from OCLC. When this happens, the specific prefixes are often stripped and replaced with the prefix “OCoLC”.
Where I am now, the OCLC number is placed in the 035 field and retains its prefixes, but “OCoLC” is also added at the beginning. Therefore, I see them multiple times a day, every day. So, I decided to get a grasp on all of these errant prefixes that I receive in my 035 field after exporting an OCLC record.
It turns out that the prefixes have almost everything to do with the length of the OCLC number.
OCLC numbers 1 through 99999999 have the “ocm” prefix. They are 8 digits with leading zeros. These records were output in WorldCat between June 28, 1981 and the 100 millionth record.
OCLC numbers 100000000 through 999999999 have the “ocn” prefix. They have 9 digits. These records are the ones that have were output beginning with the 100 millionth record. OCLC added this prefix in an update in November 2006.
OCLC numbers that are 1000000000 and higher have the “on” prefix. These have 10 or more digits. This prefix was added in July 2013 in anticipation of the 1 billionth record.
So, there you have it: those prefixes actually give us the approximate time frame of when the item was catalogued in OCLC. Not necessarily the age of the item, of course, but when a cataloguer took the time to create an original record for the item in hand.
I had figured that those prefixes meant something, but now that I know what they mean, I am kind of loathe to ever remove them, which is not something that I currently do anyway. I find the history of a record interesting and this adds another piece of information.
Matilda Davis-Northrup, Upper Arlington Public Library