- DATABASE MANAGEMENT SYSTEMS
You know that a database is a collection of logically related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals. There’s nothing new about data bases—early ones were chiseled in stone, penned on scrolls, and written on index cards, But now data bases are commonly recorded on magnetized media, and programs are required to perform the necessary storage and retrieval operations.
You’ll see in the following pages that complex data relationships and linkages may be found in all but the simplest databases. The system software package that handles the difficult tasks associated with creating, accessing, and maintaining data base records is called a data base management system (DBMS). The programs in s DBMS package establish an interface between the database itself and the users of the database. (These users may be applications programmers, managers and others with information needs and various OS programs.)
ADBMS can organize, process, and present selected data elements from the database. This capability enables decision makers to search, probe, and query data bade contents in order to extract answers to nonrecurring and unplanned questions that aren’t available in regular reports. These questions might initially be vague and poorly defined, but people can “browse” through the database until they have the needed information. In short, the DBMS will “manage” the stored data items and assemble the needed items from the common database in response to the queries of those who aren’t programmers. In a file-oriented system, users needing special information may communicate their needs to a programmer, who, when time permits, will write one or more programs to extract the data and prepare the information. The availability of a DBMS, however, offers users a much faster alternative communications path.
Sequential, direct, and other file processing approaches are used to organize and structure data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquires for information. This means that the DBMS is able to structure and tie together the logically related data from several large files.
Logical Structures. Identifying these logical relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations:
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