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数据模型由,和组成。

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R1(A,B,C,D),F={A →C,DA →B},则R1属于具有;R2(M,N,P),F={M →N,M →P},则R2属于。

当数据的____映像,保持应用程序不变,这是指数据的物理独立性。

设有一个学生课程数据库,包括如下关系:S C SC请用关系代数表达式查询如下问题:①查询选修了操作系统或数据库课程的学生学号和姓名;②查询年龄在18~23岁之间的女生的学号、姓名和年龄;③查询选修了数据库课程的学生的学号、姓名和成绩

Fill in the gaps with words or phrases given in the box. (填字母；填单词或短语所对应字母)A. buzzingB. mechanical C. implied D. decentE. stumbled into F. miniatureG. leap H. cultural/culture I. ironic J. abnormalK. Shuddering L. indication1) Students from countries such as China, which has a drastically different culture and language from the US, have to absorb a great deal of _____________ shock when they first arrive.2) Persistent(持续的)headache can be a(n) _ of a serious problem, so do not hesitate to contact your doctor.3) A _ garden takes little space but adds much beauty to the landscape.4) It is more than a little _ that some insurance companies can't even ensure their own survival.5)This former chemistry student ________ the baking business when he took a part-time job at a bakery and learned the art of bread making in the summer time.6) I'll buy whichever _ car model that comes first for a good price.7) Help! A bee is _ in my ear!8) Some experts say the weather recently experienced by China was caused by El Nino.9) The spokesperson read the statement by the White House in a dry tone.10) in the cold darkness I hoped my husband would come for me soon.11) Mary did not actually say that she was going abroad, but she certainly that she was.12) Bob knows little about European art and he is a prudent(谨慎的)guy. I don't think he is going to take a _ in the dark.