Core Data: Transient Properties on NSManagedObject

Transient properties are properties on a NSManagedObject that are not persisted to the object store. They are calculated at runtime, usually on the basis of other property values. The classic example would be for a `Person` object, generating a `fullName` property that is not persisted to the object store as both `firstName` and `lastName` are, so it can be composed at runtime.