Data Management - Part VII (Database Management System)

The Database management System is the software that handles all access to the database. Let us now examine the functions of the DBMS In a little more detail. Those function will include support for at least all of the following function.

Data definitions:

The DBMS must be able to accept data definitions in source form and convert them to the appropriate object form. In other words, the DBMS must include language processor components for each of the various data definition languages (DDLs). The DBMS must also "understand" the DDL definitions in the sense that, for example it "understands" that employee external records include a salary field; it must then be able to use this knowledge in interpreting and responding to user requests

Data Manipulation :

The DBMS must be able to handle requests from the user to retrieve. update, or delete existing data in the database, or to add new data to the database. In other words, the DBMS must include a data manipulation language (DML) processor component in general database request must be planned or unplanned":

• A planned request is one for which the need was foreseen well in advance of the time at which the request is actually to be executed. The DBA will probably have tuned the physical database design in such a way as to guarantee good performance for such requests.
• An unplanned request, by contrast, is an ad-hoc query, i.e., a request for which the need was not seen in advance. The physical database design might or might not be ideally suited for the specific request under consideration. In general, obtaining the best possible performance for unplanned request represents a significant challenge for the DBMS.

Planned request are characteristic of operational or production applications, while unplanned requests are characteristic of a decision support applications. Further more planned request will typically be issued from pre-written application programs, whereas unplanned requests, by definition, will be issued interactively

Data security and integrity :

The DBMS must monitor user requests and reject any attempts 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 data (meta data ). The dictionary might even 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.

Performance:

It goes without saying that the DBMS should perform all of the function identified above as efficiently as possible.