问题 单项选择题

下列关系模型中术语解析不正确的是( )。

A.记录,满足一定规范化要求的二维表,也称关系

B.字段,二维表中的一列

C.数据项,也成分量,是每个记录中的一个字段的值

D.字段的值域,字段的取值范围,也称为属性域

答案

参考答案:A

解析:表中的每一横行称为一个记录,也称元组。

选择题
单项选择题

Although there are many skillful Braille readers, thousands of other blind people find it difficult to learn that system. They are thereby shut (1) from the world of books and newspapers, having to (2) on friends to read aloud to them.

A young scientist named Raymond Kurzweil has now designed a computer which is a major (3) in providing aid to the (4) .His machine, Cyclops, has a camera that (5) any page, interprets the print into sounds, and then delivers them orally in a robot-like (6) through a speaker. By pressing the appropriate buttons (7) Cyclops’s keyboard, a blind person can "read" any (8) document in the English language.

This remarkable invention represents a tremendous (9) forward in the education of the handicapped. At present, Cyclops costs $ 50,000. (10) , Mr. Kurzweil and his associates are preparing a smaller (11) improved version that will sell (12) less than half that price. Within a few years, Kurzweil (13) the price range will be low enough for every school and library to (14) one. Michael Hingson, Director of the National Federation for the Blind, hopes that (15) will be able to buy home (16) of Cyclops for the price of a good television set.

Mr. Hingson’s organization purchased five machines and is now testing them in Maryland, Colorado, Iowa, California, and New York. Blind people have been (17) in those tests, making lots of (18) suggestions to the engineers who helped to produce Cyclops.

"This is the first time that blind people have ever done individual studies (19) a product was put on the market," Hingson said. "Most manufacturers believed that having the blind help the blind was like telling disabled people to teach other disabled people. In that (20) , the manufacturers have been the blind ones.

20()

A.occasion

B.moment

C.sense

D.event