Data independence

Data independence ( engl.: data independence ) is a term used in computer science that describes the degree to which a user or an application program can access the data of a database system without knowing 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, unchanging interface, which hides the implementation of data storage and data access from the user interface, so you can change this implementation and remain transparent such changes for users of the interface. This is the principle of abstract data types similarly. A distinction in database systems between physical and logical data independence.

Physical Data Independence

Physical data independence have database systems in which changes to the physical storage or the access structure ( for example, the application 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 can offer no physical data independence of access paths due to strong binding. The currently dominant relational database systems, however, meet physical data independence. Edgar F. Codd, who laid the foundations of relational database systems, formulated over 300 requirements that must comply with relational database systems; 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 search changes are made ​​" ( German: " The DBMS allows a suitably authorized user changes to the memory or the access structure or render in both - for example, for performance reasons, application programs remain logically unimpaired when such. changes are made ").

Logical Data Independence

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