Model : Finally, the Model object defines the entire database build procedure. It is comprised of a set of Entities and a set of Generators. When a Model is run, it uses the information in the Entities to create the schema graph and to instantiate the empty database tables. Then, it uses the information from each Generator's Query and Load objects to compute the order in which the Gens need to be run, thereby creating the ETL graph. Finally, it executes each Generator's Query, Pyblock, and Loads steps to actually populate the database.