Provides an object representation of the data a system must deal with.

Provides a method to store and query against the data in the domain object model.

Each concrete class in the domain object model has a corresponding table in the underlying database schema. When the object model is persisted to the database, each object is written to a row in the corresponding table.

Each class in the domain object model, whether abstract or concrete, has a corresponding table containing the data items defined in that class. Tables associated with a subclass are linked within the database, via primary key relations, with the table associated with their superclass.