1. Databases change over time.

2. The information in a database at a particular point in time is called an instance of the database.

3. The overall design of the database is called the database scheme.

4. Analogy with programming languages:

• Data type de nition - scheme
• Value of a variable - instance

5. There are several schemes, corresponding to levels of abstraction:

• Physical scheme
• Conceptual scheme
• Subscheme (can be many)