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A persistent store is a repository in which managed objects may be stored. You can think of a persistent store as a database data file where individual records each hold the last-saved values of a managed object. Core Data offers three native file types for a persistent store: binary, XML, and SQLite. You can implement your own store type if you want Core Data to interoperate with a custom file format or server. Core Data also provides an in-memory store that lasts no longer than the lifetime of a process
The entities in a store are defined by the managed object model used to create it. If you change the model in your application, you cannot open any stores you created with the original model. Instead, you must first migrate the contents of the store to the new format.