Data independence

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Data Independence (English data independence ) is a term used in computer science that describes the degree to which a user or application program to the data of a database system to know can access without details of the system technical implementation of data storage and data access. Data independence can be achieved by the database management system (DBMS) by providing a well-defined, unchangeable interface , which hides the implementation of data storage and data access from the user of the interface, so that this implementation can be changed and such changes remain transparent for the user of the interface . This is analogous to the principle of the abstract data types . In database systems, a distinction is made between physical and logical data independence.

Physical data independence

Physical data independence is demonstrated by database systems in which changes to the physical memory or access structure (for example the creation or removal of an index structure ) have no effect on the logical structure of the database , the database schema . Network-like and hierarchical database systems cannot offer any physical data independence due to their strong connection to access paths. The relational database systems predominant today, on the other hand, are physically independent of data. Edgar F. Codd , who laid the foundations for relational database systems, formulated over 300 requirements that relational database systems must meet; physical data independence is one of them. Codd formulated physical data independence as follows:

"Physical Data Independence: The DBMS permits a suitably authorized user to make changes in storage representation, in access method or in both - for example, for performance reasons. Application programs remain logically unimpaired whenever any such changes are made. "

“The DBMS allows an appropriately authorized user to make changes to the storage or the access structure or both - for reasons of performance, for example. Application programs remain logically unaffected when such changes are made. "

Logical data independence

Logical data independence means that applications are immune to changes made to the database schema. Logical data independence can only be implemented for simple modifications to the database schema; for example, changes to an attribute can be hidden from the application program using a view definition .

See also

literature

  • Alfons Kemper, André Eickler: Database systems. Oldenbourg Verlag, 2004, ISBN 3-486-25706-4 , p. 20

Individual evidence

  1. ^ Edgar F. Codd: The Relational Model for Database Management: Version 2 . Addison-Wesley, 1990