Database Concepts › Logical Database Description

Logical Database Description

A CA IDMS database description consists of three components:

• A logical description represented by a schema reflecting the entity types and relationships contained within the database.
• A physical description specifying how the data is physically stored on direct access storage devices (DASD).
• A program's view, represented by a subschema, which is often a subset of the schema types and relationships.

By separating the logical and physical definitional components, it is possible for a single schema to describe multiple physical database instances. For example, a single schema can describe both the test database used for application development and the QA database used for staging applications into production.

Data independence is achieved by allowing a program to view the database differently from how it is defined in the schema.