1. We have been looking mostly at the higher-level models of a database. At the conceptual or logical level the database was viewed as

• A collection of tables (relational model).
• A collection of classes of objects (object-oriented model).

2. The logical model is the correct level for database users to focus on. However, performance depends on the effciency of the data structures used to represent data in the database, and on the effciency of operations on these data structures.