Logical data independence is the ability to modify the logical schema without causing application programs to be rewritten.The new changes are absorbed by mapping techniques. It means we change the physical storage/level without affecting the conceptual or external view of the data. Modifications at the physical level are occasionally necessary to improve performance. Physical data independence is the ability to modify the physical schema without causing application programs to be rewritten.There are two levels of data independence, they are Physical data independence and Logical data independence. The ability to modify schema definition in one level without affecting schema of that definition in the next higher level is called data independence. This feature was not available in the file oriented approach. It also means we can change the structure of a database without affecting the data required by users and programs. It means we can change the conceptual schema at one level without affecting the data at another level. One of the highest advantage of databases is data independence. Physical data independence is present in most databases and file environment in which hardware storage of encoding, exact location of data on disk, merging of records, so on this are hidden from user. In this, internal schema changes may be required due to some physical schema were reorganized here. In this, external schema does not change. The logical scheme stays unchanged even though the storage space or type of some data is changed for reasons of optimization or reorganization. View level data independence: always independent no effect, because there doesn't exist any other level above view level.ĭata independence can be explained as follows: Each higher level of the data architecture is immune to changes of the next lower level of the architecture.For example, a change to the internal schema, such as using different file organization or storage structures, storage devices, or indexing strategy, should be possible without having to change the conceptual or external schemas. Physical data independence: The ability to change the physical schema without changing the logical schema is called physical data independence.For example, the addition or removal of new entities, attributes, or relationships to the conceptual schema or having to rewrite existing application programs. Logical data independence: The ability to change the logical (conceptual) schema without changing the External schema (User View) is called logical data independence.There are three types of data independence: The application should not be involved with these issues since, conceptually, there is no difference in the operations carried out against the data. Physical data independence deals with hiding the details of the storage structure from user applications. The physical structure of the data is referred to as "physical data description". Logical data independence indicates that the conceptual schema can be changed without affecting the existing schemas. 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. The logical structure of the data is known as the 'schema definition'.
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