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various functions of DBMS

 various functions of DBMS
      • Data definition: The DBMS must be able to accept data definitions (external schema , the conceptual schema, the internal schema, and all associated mappings) in source form and convert them to the appropriate object form.
      • Data manipulation: The DBMS must be able to handle requests from the users to retrieve, update, or delete existing data the database, or to add new data to the database. In other words, the DBMS must include a data manipulation language (DML) processor component.
      • Data security and integrity: The DBMS must monitor user requests and reject
any attempt to violate the security and integrity rules defined by the DBA.
      • Data recovery and concurrency: The DBMS - or else some other related software component, usually called the transaction manager - must enforce certain recovery and concurrency controls.
      • Data Dictionary: The DBMS must provide a data dictionary function. The data dictionary can be regarded as a database in its own right (but a system database, rather than a user database). The dictionary contains “data about the data” (sometimes called metadata) - that is, definitions of other objects in the system - rather than just”raw data.” In particular, all the various schemas and mapping (external, conceptual, etc.) will physically be stored, in both source and object form, in the dictionary. A comprehensive dictionary will also include cross- reference information, showing, for instance, which programs use which pieces of the database, which users require which reports, which terminals are connected to the system, and so on. The dictionary might even - in fact, probably should — be integrated into the database it defines, and thus include its own definition. It should certainly be possible to query the dictionary just like any other database, so that, for example, it is possible to tell which programs and or users are likely to be affected by some proposed change to the system.
      Performance: It goes without saying that the DBMS should perform all of the functions identified above as efficiently as possible.

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