In a data model, it is important to distinguish between the description of the database and the database itself. The description of a database is called the database schema, which is specified during database design and is not expected to change frequently
Most data models have certain conventions for displaying schemas as diagrams. A displayed schema is called a schema diagram.
A schema diagram displays only some aspects of a schema, such as the names of record types and data items, and some types of constraints
The data in the database at a particular moment in time is called a database state or snapshot. It is also called the current set of occurrences or instances in the database