There is only one file type that uses the .MOM extension:
Managed Object Model
Data model created with Apple's Xcode development software; stores a Core Data model that is generated from a program's code; saved in an archived version of the NSManagedObjectModel format.
MOM files can be imported into Xcode Design Tools by selecting Design→Data Model→Import... from the Xcode menu bar.
Updated: April 12, 2009