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External view or User view/View Level

The generalized architecture of DBMS is called ANSI/SPARC model. The architecture is divided into three levels:

It is the highest level of data abstraction. This includes only those portions of database of concern to a user or Application program. Each user has a different external view and it is described by means of a scheme called external schema.

Conceptual view/Logical Level

All the database entities and the relationship among them are included. One conceptual view represents the entire database called conceptual schema.

Internal view/Physical Level

It is the lowest level of abstraction, closest to the physical storage method. It describes how the data is stored, what is the structure of data storage and the method of accessing these data. It is represented by internal schema.

View Level …Defined by User


Instances and Schemas


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 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
  • 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 parts do not seriously influence others.


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Physical Level
Logical Level

Defined by DBA for optimization


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