2. 计算机
  3. A database system is a collection of interrelated data and a set of programs that allow users to access and modify these data．A

A database system is a collection of interrelated data and a set of programs that allow users to access and modify these data．A

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问题 A database system is a collection of interrelated data and a set of programs that allow users to access and modify these data．A major purpose of a database system is to provide users with an____①____ view ofthe data．That is，the system hides certain details of how the data are stored and maintained．For the system to be usable,it must retrieve data ____②____．The need for efficiency has led designers to use complex data ___③_____ to represent data in the database．Since many database—system users are not computer trained，developers hide the complexity from users through several levels of abstraction，to simplify users’interactions with the system．Physical level is the lowest level ofabstraction that describes ____④____ the data are actually stored．Logical level is the next-higher level of abstraction that describes___⑤_____data are stored in the database，and what relationships exist among those data．View level is the highest level of abstraction that describes only part of the entire database．
④
选项 A、how
B、what
C、which
D、when
答案A
解析
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