Earlier each database management system had its own

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Unformatted text preview: ing access controls to the various tables, records, and fields for different categories of users to protect the privacy of sensitive data items from unauthorized users. 6. Defining the logical relationships among the various data elements of the database. In short, virtually everything about the database structure is included in its schema. It is possible to generate complete description of a database from its schema. This description, in turn, can be used by systems analysts ii defining new applications on the database. Database systems are typically installed and coordinated by an individual called the database administrator. He/she has the overall authority to establish and control data definitions and standards. He/she is responsible for determining the relationships among data elements, and for designing the database security system to guard against unauthorized use. He/she also trains and assists applications programmers in the use of the database. A data dictionary is developed and used in a database to document and maintain the data definitions. It is automatically created/updated by the DDL module of the DBMS as the database schema is defined or changed. Data Manipulation Language (DML) Once the structure of a database (database schema) has been defined, the database is ready for the entry and manipulation of data. The data manipulation language {DML) includes all the commands that enable the users to enter and minipulate the data. With these commands, the user can do such things as add new records to the database, navigate through the existing records, view the contents of the various fields of a record, modify the contents of one or more fields of a record, delete an existing record, and sort the records in a desired sequence. In some DBMS, the data definition language and the data manipulation language are combined together, while in others, they are supported as separate DBMS components. Query Language Although it is possible to navigate through a database one record at a time to extract the desired informatio...
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This document was uploaded on 04/07/2014.

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