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【正文】 Database Management Systems 3th Edition Wiley 2021 512 A introduction to Database Management System Raghu Ramakrishnan A database sometimes spelled data base is also called an electronic database referring to any collection of data or information that is specially anized for rapidsearch and retrieval by a puter. Databases are structured to facilitate the storageretrieval modification and deletion of data in conjunction with variousdataprocessing operations .Databases can be stored on magic disk or tape opticaldisk or some other secondary storage device. A database consists of a file or a set of files. The information in these files maybe broken down into records each of which consists of one or more fields. Fields arethe basic units of data storage and each field typically contains informationpertaining to one aspect or attribute of the entity described by the database . Usingkeywords and various sorting mands users can rapidly search rearrange groupand select the fields in many records to retrieve or create reports on particularaggregate of data. Complex data relationships and linkages may be found in all but the simplestdatabases .The system software package that handles the difficult tasks associatedwith creating accessing and maintaining database records is called a databasemanagement programs in a DBMS package establish an interfacebetween the database itself and the users of the database.. These users may beapplications programmers managers and others with information needs and variousOS programs. A DBMS can anize process and present selected data elements form thedatabase. This capability enables decision makers to search probe and querydatabase contents in order to extract answers to nonrecurring and unplanned questionsthat aren痶 available in regular reports. These questions might initially be vagueand/or poorly defined but people can “browse” through the database until they havethe needed information. In short the DBMS will “manage” the stored data items andassemble the needed items from the mon database in response to the queries ofthose who aren’t programmers. A database management system DBMS is posed of three major parts:1astorage subsystem that stores and retrieves data in files2 a modeling andmanipulation subsystem that provides the means with which to anize the data andto add delete maintain and update the data3and an interface between the DBMSand its users. Several major trends are emerging that enhance the value and usefulnessof database management systems Managers: who require more uptodata information to make effective decision Customers: who demand increasingly sophisticated information services and more current informati
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