问题 单项选择题

多用户的数据库系统的目标之一是使它的每一个用户好像面对着一个单用户的数据库一样使用它,因此数据库系统必须进行______。

A) 并发控制
B) 完整性控制
C) 安全性控制
D) 可靠性控制

答案

参考答案:A

解析: 并发控制功能能够保证并发操作的有效进行。它允许多个用户同时共享同一条记录的数据项;保证一个记录在某一时刻只能有一个用户进行修改操作,若多个用户都想修改同一记录,必须首先竞争到“锁定”权限后,才能修改;修改完成后,该程序应“解锁”该记录,让其他用户再竞争。

判断题
单项选择题

Oxford and Cambridge University Boat Clubs have both taken the opportunity to travel to Spain this month to train in less testing weather conditions than those which have, quite literally, already blown around the UK in January of 2007.

Each group of athletes has been focused on training to the maximum, working on technique and molding themselves into two potential fighting units per Club for the 2007 Boat Race, sponsored by Xchanging. One set will be in the Blue Boat for each club and one set will race as reserves in Isis, for Oxford, and Goldie, for Cambridge.

In these modern times, the Head Coach for each club has a huge input on selection even though the crew is still named by the President. Just twenty years ago the balance was not quite the same.

The year 1987 will always be remembered in the history of this great Race as the year of the "mutiny" at Oxford. It is a tale which has since been retold and reworked in both a book and a movie.

This was the season for which mature Scottish student, Donald Macdonald, was elected President, having all ready won a Blue in 1986. Macdonald re-appointed Daniel Topolski (now a renowned rowing journalist and broadcaster) as Chief Coach.

Part of the 1986/87 squad at Oxford included American Chris Clark, now a coach at an American University, and four fellow US internationals.

Allegedly, a split appeared in the squad between the American quintet, all experienced and leading oarsmen, and those rowers closest to Macdonald. The Scot’s group were happy to follow Topolski’s regime whilst the others were not so sure.

Following a contentious seat racing trial in January of 1987, Topolski decided to move Clark to the bow-side of the beat. Clark disagreed. Topolski held firm. As a result Clark and his "group" within the squad decided not to ROW and sought a takeover.

The squabble was played out extensively in the UK national media and caught the public imagination. MacDonald sought support from the college captains and eventually won a vote of confidence by 28 votes to 11.

Without the Americans, the Oxford crew was immediately considered a lost cause. Cambridge were overwhelming favorites to win.

As it turned out, though, this was a Race which would prove why sport, and particularly The Boat Race, can be so fascinating.

The split seemed to be caused by the disagreement between ().

A. Topolski and Clark

B. MacDonald and Clark

C. MacDonald and Topolski

D. the Scottish students and the American oarsmen