Chapter 8. Versioning and Migrating Data
As you develop Core Data–based applications, you usually don't get your data model exactly right the first time. You start by creating a data model that seems to meet your application's data needs, but as you progress through the development of the application, you'll often find that your data model should change to serve your growing vision of what your application will do. During this stage of your application's life, changing your data model to match your new understanding of the application's data poses little cost: your application will no longer launch, crashing on startup with the message:
The model used to open the store is incompatible with the one used to create the store
You resolve this issue ...