分布式数据库系统有哪些优点和缺点？
参考答案：
分布式数据库系统的优点：
（1）具有灵活的体系结构
（2）适应分布式的管理和控制机构
（3）经济性能优越
（4）系统的可靠性高、可用性好
（5）局部应用的响应速度快
（6）可扩展性好，易于集成现有系统。
分布式数据库系统的缺点：
（1）系统开销大，主要花在通信部分；
（2）复杂的存取结构，原来在集中式系统中有效存取数据的技术，在分布式系统中都不再适用；
（3）数据的安全生和保密性较难处理。
Passage One
| Opinion polls are now beginning to show an unwilling general agreement that, whoever is to blame and whatever happens from now on, high unemployment is probably here to stay. This means we shall have to find ways of sharing the available employment more widely. But we need to go further. We must ask some fundamental questions about the future of work. Should we continue to treat employment as the norm Should we not rather encourage many other ways for self-respecting people to work Should we not create conditions in which many of us can work for ourselves, rather than for an employer Should we not aim to revive the household and the neighborhood, as well as the factory and the office, as centers of production and work The industrial age has been the only period of human history in which most people’s work has taken the form of jobs. The industrial age may now be coming to an end, and some of the changes in work patterns which it brought may have to be reversed. This seems a discouraging thought. But, in fact, it could offer the prospect of a better future for work. Universal employment, as its history shows, has not meant economic freedom. Employment became widespread when the enclosures (圈地运动) of the 17th and 18th centuries made many people dependent on paid work by depriving them of the use of the land, and thus of the means to provide a living for themselves. Then the factory system destroyed the cottage industries and removed work from people’s homes. Later, as transport improved, first by rail and then by road, people traveled longer distances to their places employment until eventually, many people’s work lost all connection with their home lives and places in which they lived. Meanwhile, employment put women at a disadvantage. It became customary for the husband to go out to paid employment, leaving the unpaid work of the home and family to his wife. All this may now have to change. The time has certainly come to switch some effort and resources away from the impractical goal of creating jobs for all, to the urgent practical task of helping many-people to manage without full-time jobs. |
As a result of the enclosures of the 17th and i8th centuries,
A．people were no longer legally entitled to own land
B．people were forced to look elsewhere for means of supporting themselves
C．people were not adequately compensated for the loss of their land
D．people were badly paid for the work they managed to find
