The Domain model will be developed in an iterative process. Instance Identification. The domain model will have two components, the E-R diagram for the database and class diagrams for messages and interactions. The Domain Model will derive from the information model and be developed in parallel to the Use Case Model and the User Interface Model. The class diagrams for the model will describe all data used in the system and a subset of this will be described in the E-R diagram which will describe the persistent data of the system that will need to be stored in a database.