A introduction to Database Management System Raghu RamakrishnanA introduction to Database Management System Raghu Ramakrishnan.doc

A?introduction?to?Database?Management?System? Raghu?Ramakrishnan? Wiley［U.S.］ A?database?(sometimes?spelled?data?base)?is?also?called?an?electronic?database??,?referring?to?any?collection?of?data,?or?information,?that?is?specially?organized?for?rapid?search?and?retrieval?by?a?computer.?Databases?are?structured?to?facilitate?the?storage,?retrieval?,?modification,?and?deletion?of?data?in?conjunction?with?various?data-processing?operations?.Databases?can?be?stored?on?magnetic?disk?or?tape,?optical?disk,?or?some?other?secondary?storage?device.? A?database?consists?of?a?file?or?a?set?of?files.?The?information?in?these?files?may?be?broken?down?into?records,?each?of?which?consists?of?one?or?more?fields.?Fields?are?the?basic?units?of?data?storage??,?and?each?field?typically?contains?information?pertaining?to?one?aspect?or?attribute?of?the?entity?described?by?the?database?.?Using?keywords?and?various?sorting?commands,?users?can?rapidly?search?,?rearrange,?group,?and?select?the?fields??in?many?records?to?retrieve?or?create?reports?on?particular?aggregate?of?data.? 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?database?records?is?called?a?database?management?system(DBMS).The?programs?in?a?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.)? A??DBMS?can?organize,?process,?and?present?selected?data?elements?form?the?database.?This?capability?enables?decision?makers?to?search,?probe,?and?query?database?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/or?poorly?defined?,but?people?can?“browse”?through?the?database?until?they?have?the?needed?information.?I