搜题请搜索小程序“爱下问搜题”
问题 填空题

在关系模式规范化过程中，若要求分解保持函数依赖，那么分解后的模式一定可以达到 3NF，但不一定能达到 _______。

答案

参考答案：BCNF 或 Boyce-Codd 范式

解析：关于模式分解的几个事实：1、分解具有无损连接性和分解保持函数依赖是两个互相独立的标准。关系模式的一个分解可能具有无损连接性，可能是保持函数依赖的，也可能是既具有无损连接性又保持函数依赖的。2、若要求分解具有无损连接性，那么模式分解一定可以达到 BCNF。3、若要求分解保持函数依赖，那么模式分解可以达到 3NF，但不一定能达到 BCNF。4、若要求分解既具有无损连接性，又保持函数依赖，则模式分解可以达到3NF，但不一定能达到BCNF。

判断题

低碳经济的实质是能源高效利用、清洁能源开发、追求绿色GDP的问题。
查看答案
单项选择题

People are indulging in an illusion whenever they find themselves explaining at a cocktail(鸡尾酒) party, say, that they are "in computers," or "in telecommunications," or "in electronic funds transfer". The implication is that they are part of the high-tech world. Just between us, they usually aren’t. The researchers who made fundamental breakthroughs in those areas are in a high-tech business. The rest of us are （） of their work. We use computers and other new technology components to develop our products or to organize our affairs. Because we go about this work in teams and projects and other tightly knit working groups(紧密联系在一起的工作小组), we are mostly in the human communication business. Our successes stem from good human interactions by all participants in the effort, and our failures stem from poor human interactions. The main reason we tend to focus on the （） rather than the human side of the work is not because it’s more （） , but because it’s easier to do. Getting the new disk drive installed is positively trivial compared to figuring out why Horace is in a blue funk(恐惧) or why Susan is dissatisfied with the company after only a few months. Human interactions are complicated and never very crisp(干脆的,干净利落的) and clean in their effects, but they matter more than any other aspect of the work. If you find yourself concentrating on the （） rather than the （）, you’re like the vaudeville character(杂耍人物) who loses his keys on a dark street and looks for them on the adjacent street because, as he explains, "The light is better there!".

rather than the （）

A．technology

B．sociology

C．physiology

D．astronomy
查看答案