Data Independence | Database Management System

Data Independence | Database Management System

Data Independence : Data Independence is isolating an upper level from the changes in the organization or structure of a lower level. For example, if changes in the file organization of a data file do not demand for changes in the functions in the DBMS or in the application programs, data independence is achieved. Thus Data Independence can be defined as immunity of applications to change in physical representation and access technique. The provision of data independence is a major objective for database Systems. Data independence is the type of data transparency that matters for a centralized DBMS. It refers to the immunity of user applications to make changes in the definition and organization of data, and vice-versa. The ability to modify a schema definition in one level without affecting a schema definition in the next higher level is called Data independence. Data Independence is one of the main advantage of the DBMS. Physical data independence deals with hiding the details of the storage structure from user applications. The application should not be involved with these issues, since there is no difference in the operation carried out against the data. The data independence and operation independence together gives the feature of Data Abstraction.

The logical structure of the data is known as the schema definition. In general, if a user application operates on a subset of the attributes of a relation, it should not be affected later when new attributes are added to the same relation. There are two types of Data Independence:

  1. Physical Data independence: The ability to change the logical Schema without changing the External schema is called Logical Data independence. It is the ability to modify the conceptual schema without causing application program to be rewritten, Logical Data Independence is more difficult to achieve than physical data independence, since program are having dependence on the logical structure of the database. Example: Addition or removal of new entities, attributes, or relationships to the conceptual schema should be possible without having to change existing external schemas or having to rewrite existing application programs.
  2. Logical Data Independence: The ability to change the physical Schema without changing the logical schema is called Physical Data Independence. It is the ability to modify the physical schema without causing application program to be rewritten. In other words, old programs do not have to be rewritten, when changes are made to physical storage structure or the physical devices on which data are stored.

Example : A change to the internal Schema, such as using different file organisation or storage Structures, Storage devices, or indexing strategy, should be possible without having to change the conceptual or external schemas.