只有能够保证分解后的关系模式与原关系模式等价,分解方法才有意义。
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若要求分解既具有无损连接性,又保持函数依赖,则模式分解一定能够达到3NF,但不一定能够达到BCNF。
A. 对
B. 错
如果一个分解保持了函数依赖,则它可以减轻或解决各种异常情况。
A. 对
B. 错
把低一级的关系模式分解为若干个高一级的关系模式的方法并往往是唯一的。
A. 对
B. 错
Please translate the following report into Chinese.To:Mrs. Zhao, Dean of Foreign Language DepartmentFrom:Mr. Niu,Teaching SecretarySubject:Buying computers and videotape recordersDear Mrs. Zhao: Upon the request of the Equipment Division of the college,we have inspected the sound laboratory of the English Department and found its present equipments unsatisfactory to students, because there are forty computers in our laboratory,but the students are almost ten times as many. The laboratory material is so short that the situation has to be improved at once. In order to enhance the effect of experiments, it is hereby recommended that twenty computers and ten videotape recorders be bought and issued to the laboratory. Niu Xinhua