我们常用的数据模型类型有层次模型、网状模型、关系模型和面向对象模型四种。()是数据库系统中最早出现的数据模型，其数据库系统的典型代表是IBM公司的IMS(Information　Management　Systems)数据库管理系统。

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One　of　the　functions　of　the(71)is　to　store　the　applications　programs　{　or　the　various　secondaries.　　The(72)may　have　similar　or　dissimilar　functions.　The　same　control　code　received　from　two　different,　secondaries　may　warrant　two　different　actions　on　the　part　of　the　host　computer.　If　the　system　so　requires,　the　host　computer　must　also　provide(73)for　the　centralized　data　and　the　software　for　database　management.　Data　information　is　normally　stored　in　auxiliary　memories　to　which　the　computer　has　ready　access.　The(74)peripherals　connected　to　the　host　computer　allow　for　human　entry　and　intervention.　As　needs　change,　application　programs　may　require　additions,　　deletions,　or　changes.　Data　link　problems　also　arise　which　are(75)the　range　of　the　computer's　programmed　capabilities.　In　such　cases,　human　entry　is　required　to　make　the　necessary　changes　to　resolve　the　existing　problems.

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