问题 问答题 简答题

试述网状数据模型的优缺点。

答案

参考答案:

网状数据模型的优点:

①能够更为直接地描述现实世界,如一个结点可以有多个双亲。结点之间可以有多种联系。

②具有良好的性能,存取效率较高。网状数据模型的缺点:

①结构比较复杂,而且随着应用环境的扩大,数据库的结构就变得越来越复杂,不利于最终用户掌握。

②网状模型的DDL、DML复杂,并且要嵌入某一种高级语言(如COBOL、C.中。用户不容易掌握,不容易使用。

完形填空

第二部分:英语知识及运用(共两节,满分35分)

第一节:完形填空(共15小题;每小题2分,满分20分)

阅读下面短文,从短文后所给各题的四个选项A、B、C和D中选出能填入相应空白处的最佳选项。

When I was walking down the street the other day, I happened to ___21______ a small brown leather purse lying on the sidewalk. I picked it up and opened it to see if I could ___22___ the owner's name. There was nothing inside it ____23______ some change and an old photo ―― a picture of a woman and a young girl of about twelve years, who looked like the woman's daughter. I put the photo back and ____24______ the purse to the police station, where I ___25_______ it to the desk sergeant. ____26______ I left, the sergeant took down my name and address ___27_______ the owner might want to write and thank me.

That evening I went to have dinner with my aunt and uncle. They ___28______ a young woman so that there would be four people at the table. Her face was familiar. I was ____29______ sure that we had not met before, but I could remember where I had seen her. In the course of conversation, however, the young woman happened to mention that she had lost her purse that afternoon. ___30______ I realized where I had seen her. She was the young girl in the photo, although she was now much older.

21. A. watch                 B. notice             C. discover                   D. find out

22. A. find                    B. learn                        C. discover                   D. work out

23. A. besides        B. except               C. except for                 D. in addition to

24. A. took                   B. brought                    C. fetched                     D. sent

25. A. offered        B. passed               C. handed                     D. returned

26. A. Before         B. When                C. While               D. As

27. A. although             B. in case                     C. for fear                    D. so that

28. A. have also invited                              B. also had invited

C. also invited                                     D. had also invited

29. A. well                   B. much                       C. quite                        D. very

30. A. All at once B. At once                    C. Immediately             D. All suddenly

单项选择题