What is the difference between merge and overlay?
When two bibliographic records are combined in Alma, either the merge or overlay method determines how the data is handled.
Merge
• Retains selected bibliographic data from both records based on predefined merge rules.
• Merge rules specify which fields to keep, modify, or discard.
• Used when you want to preserve local enhancements or key metadata from the original record.
Overlay
• Completely replaces the old bibliographic record with the new one.
• All data from the old record is discarded—nothing is merged.
• Used when importing a full, authoritative record to replace a brief or temporary one.
Example Use Cases:
• Merge: You import a record from an external source but want to keep local notes and call numbers from the existing record.
• Overlay: You receive a full MARC record from a vendor and need to replace an incomplete placeholder record.
