MILLENNIUM BIBLIOGRAPHIC RECORD OVERLAY DEFINITIONS
- Incoming Record – The new OCLC record that will replace the old record in Millennium.
- Target Record – The record in Millennium that is to be overlaid.
Bibliographic overlay can be done by anyone with OCLC Connexion authorization. While this means that catalogers can now do their own overlays (unlike GLADIS), it also means that catalogers must be especially aware of potential problems related to overlay, and how to avoid these problems.
- Overlay should only be done where absolutely necessary.
- When overlaying, special care should be taken to prevent loss of data from the target record.
- When overlaying, catalogers need to be aware of the potential for field duplication in target records.
Bibliographic record overlay can happen under two scenarios:
1. OCLC Number Match –
Start by searching for the item in Millennium. See OCLC number duplication.
An OCLC number match is predicated by the presence of a matching OCLC number in MARC tag 001 in the target record. OCLC numbers in MARC tag 035 are ignored. Records with OCLC numbers in MARC tag 035 should be referred for resolution to BadCat or the relevant self-cataloging unit, since we no longer store OCLC numbers in this field.
If an incoming record’s OCLC number matches an OCLC number in a bibliographic record already in Millennium, overlay will happen, whether the cataloger intends it or not. This is why it’s critical to check Millennium first to see what is already in the catalog.
Where a cataloger intends to overlay a record already in Millennium, if the intended target contains the same OCLC number as in the record to be sent from OCLC, merely exporting the record will cause it to overlay – the cataloger need not include the target record bibliographic record number in MARC tag 907.
The OCLC export load table will:
- Create a new record when there is no target record with a matching OCLC number.
- Overlay the target record where there is an OCLC number match.
- Reject the incoming record from overlay where there are 2 or more records in Millennium with the same OCLC number.
Anytime there is more than one record in Millennium with the same OCLC number, these records should be merged. These merges can be done by the cataloger where appropriate; otherwise they can be referred for resolution to BadCat or the relevant self-cataloging unit.
2. Forced Overlay with Bibliographic Record Number –
Start by searching for the item in Millennium. See instructions for avoiding OCLC number duplication. When this step is skipped, OCLC number duplication can occur.
Forced overlay using the target bibliographic record as a match point in the incoming record MARC tag 907 should only be used under two circumstances:
- The target record does not have an OCLC number in MARC tag 001 (e.g., the target record is an on-order record or a preliminary in-process record).
The target record contains an OCLC number in MARC tag 001 that is different from that of the incoming record.
IMPORTANT: When overlaying a target record that contains an OCLC number in MARC tag 001 that is different from that of the incoming record, remove target record holdings from OCLC! Since the target record is being replaced, there can be no automated OCLC holdings removal; it must be done manually. Use detailed OCLC number change instructions for this process when doing this work.
WHEN TO OVERLAY
Millennium bibliographic records should only be overlaid where necessary, since overlay introduces significant room for problems, some catastrophic. In general, overlay should only happen where OCLC copy is significantly better than what is already in Millennium, AND, it is more efficient to overlay the target record rather than make bibliographic edits to bring our local record copy in line with Master Record copy.
- Upgrading low level, or brief records, with full copy.
- Target record is full level, but significant edits should be made to the bibliographic record (contents note, headings, other access points). In this case, the OCLC Master Record should be edited and replaced, and the target Millennium record overlaid with new copy.
Otherwise, do NOT overlay.
CAUTIONS AND CLEAN-UP
Millennium catalog records are created and maintained by main cataloging technical services, self-cataloging units, affiliated libraries, and regional storage participants. Catalogers must be aware that data input by another cataloging “group” needs to be preserved from overlay.
1. Data Loss – Whenever a record is overlaid, there is the potential for data loss. Target records should always be carefully reviewed against the incoming record to be sure that no data loss will occur. Where field loss could potentially occur, the cataloger should make note of this by including relevant data as part of the incoming record, as well as enhancing OCLC Master Record copy with this data where applicable.
2. Field Protection – Some MARC tags in Millennium bibliographic records are “protected” from overlay by the load table. These are critical, non-negotiable fields which must be protected from incoming copy. The MARC tags can be found at:
Where a MARC tag is protected from overlay, there is the potential for duplication following overlay. If, for example, the target record contains an 856 for TOC data, and if the incoming record also contains this field, the result can be that there will be two identical MARC 856 fields with TOC data. Where this happens, the cataloger needs to delete one of these fields from the overlaid record in Millennium.
While on the one hand this duplication of data is unwanted, it negates the possibility that loss of these critical fields will occur in target records. In the case of URLs with paid electronic access, the loss of this data would be catastrophic.
3. Incorrect Record Replacement – OCLC number matching and subsequent record overlay will never result in incorrect record replacement. However, where using the bibliographic record number for record overlay, extreme caution must be exercised to prevent an incoming record from overlaying an unintended target:
- When cataloging, always search Millennium first before searching OCLC to see what we hold in our local catalog.
- If you find that a different OCLC record should overlay a target record in Millennium, or that the target record does not have an OCLC number, use the copy and paste function to input the bibliographic record number into MARC tag 907 in the incoming record. NEVER type this number by hand; an error in the keying of this record will mean that your incoming record will overlay an unintended target!
Author: Jim Lake
Approval Group: Cataloging and Metadata Council
Update Group: Cataloging & Metadata Council
Last updated date: 07/03/14
Data Control Unit > BadCat or self-cat unit
Thu, 07/03/2014 – 12:08 — Michael Meacham
Changed two references to Data Control Unit to “BadCat or the relevant self-cataloging unit”.
Removed references to the 079 field
Tue, 07/09/2013 – 09:57 — epinto
Since we’re no longer carrying OCLC Institution Record numbers in our records, the 079 field is no longer relevant for OCLC number matching.
Tue, 07/09/2013 – 09:57 — epinto
Added link to OCLC/Millennium sending doc which has procedures for changing the OCLC number in a record, and added reminders to check Millennium first before sending a record to avoid duplicates.
Thu, 07/21/2011 – 13:11 — Charis Takaro
Moving definitions that might have relevance beyond this doc to the glossary.