What is instances & schemas in Database Managment System(DBMS)?, Physical Schema & Logical Schema in DBMS, What is Physical Data Independence ?
Schema definitionIt is the logical structure of the database e.g., the database consists of information about a set of customers and accounts and the relationship between them)
Analogous to type information of a variable in a program
Physical schema: database design at the physical level is called physical schema
Logical schema: database design at the logical level is called logical schema
Instance – It is the actual content of the database at a particular point in time
Analogous to the value of a variable
What is Physical Data Independence ?
It is 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 parts do not seriously influence others.
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