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1、DatabaseSystems1.FundamentalConceptsofDatabaseDatabaseanddatabasetechnologyarehavingamajorimpactonthegrowinguseofcomputers.Itisfairtosaythatdatabasewillplayacriticalroleinalmostallareaswherecomputersareused,includingbusiness,engineering,medicine,law,education,andlibraryscience,toname
2、afew.Theword"database"isinsuchcommonusethatwemustbeginbydefiningwhatadatabaseis.Ourinitialdefinitionisquitgeneral.Adatabaseisacollectionofrelateddata.Bydata,wemeanknownfactsthatcanberecordedandthathaveimplicitmeaning.Forexample,considerthenames,telephonenumbers,andaddressesofallthepe
3、opleyouknow.Youmayhaverecordedthisdatainanindexedaddressbook,oryoumayhavestoreditonadisketteusingapersonalcomputerandsoftwaresuchasDBASEIIIorLotus1-2-3.Thisisacollectionofrelateddatawithanimplicitmeaningandhenceisadatabase.Theabovedefinitionofdatabaseisquitegeneral;forexample,wemayco
4、nsiderthecollectionofwordsthatmakeupthispageoftexttoberelateddataandhenceadatabase.However,thecommonuseofthetermdatabaseisusuallymorerestricted.Adatabasehasthefollowingimplicitproperties:.Adatabaseisalogicallycoherentcollectionofdatawithsomeinherentmeaning.Arandomassortmentofdatacann
5、otbereferredtoasadatabase..Adatabaseisdesigned,built,andpopulatedwithdataforaspecificpurpose.Ithasanintendedgroupofusersandsomepreconceivedapplicationsinwhichtheseusersareinterested..Adatabaserepresentssomeaspectoftherealworld,sometimescalledtheminiworld.Changestotheminiworldarerefle
6、ctedinthedatabase.Inotherwords,adatabasehassomesourcefromwhichdataarederived,somedegreeofinteractionwitheventsintherealworld,andanaudiencethatisactivelyinterestedinthecontentsofthedatabase.Adatabasecanbeofanysizeandofvaryingcomplexity.Forexample,thelistofnamesandaddressesreferredtoea
7、rliermayhaveonlyacoupleofhundredrecordsinit,eachwitha5simplestructure.Ontheotherhand,thecardcatalogofalargelibrarymaycontainhalfamillioncardsstoredunderdifferentcategories-byprimaryauthor’slastname,bysubject,bybooktitle,andthelike-witheachcategoryorganizedinalphabeticorder.Adatabaseo
8、fevengreater
