Instance and Schema:-

Similar to types and variables in programming languages:-

Schema:– The logical structure of the database

Example: The database consists of information about a set of clientele and accounts and the connection between them)

Analogous to type information of a variable in a program.

Physical schema: Database design at the physical level

Logical schema: Database design at the logical level

Instance:- The actual content of the database at a particular point in time

Analogous to the value of a variable.

Physical Data Independence:– the ability to modify the physical schema without Changing the logical schema

Applications depend on the logical schema

In general, the interfaces between the various levels and components should be well defined so that changes in some part do not seriously influence others.