Database: Difference between revisions

Revision as of 11:28, 21 July 2004

Revision as of 17:38, 11 August 2004

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In recent years, the [[object-oriented]] paradigm has been applied to databases as well, creating a new programming model known as [[object database|object databases]]. These databases attempt to overcome some of the difficulties of using objects with the SQL DBMSs. An object-oriented program allows objects of the same type to have different implementations and behave differently, so long as they have the same interface ([[polymorphism_(computer_science)|polymorphism]]). This doesn't fit well with a SQL database where user-defined types are difficult to define and use, and where the Two Great Blunders prevail: the identification of classes with tables (the correct identification is of classes with types, and of objects with values), and the usage of pointers.

A variety of ways have been tried for storing objects in a database, but there is little consensus on how this should be done. Implementing object databases undo the benefits of relational model by introducing pointers and making ad-hoc queries more difficult. This is because they are essentially adaptations of obsolete network and hiearchicalhierarchical databases to object-oriented programming. As a result, object databases tend to be used for specialized applications and general-purpose object databases have not been very popular. Instead, objects are often stored in SQL databases using complicated mapping software. At the same time, SQL DBMS vendors have added features to allow objects to be stored more conveniently, drifting even further away from the relational model.

== Applications of databases ==