Database schema and Schema diagram

Database schema and Schema diagram

In any data model, it is important to distinguish between the description of the database and the database itself. The description of a database is called a database schema, which is specified during database design and its not expected to changefrequently. 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 contraints. Other aspects are not specified in the schema diagram.

The actual data in a database may change quite frequently. The data in the database at a paritcular moment in time is called a database state or snapshot. It is also called current set of occourences or instances in the database.

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