信息网络的革命性突破 ,使人们的生存空间为人们创造的网络空间所挤占。全球国际互联网的建成使人们从网络终端可以及时得到所需要的任何信息。当我们进入计算机网络 ,总希望网上的信息越多越好 ,找得越准越好 ,从而获得更多的信息。然而随着网络信息的增多 ,要检索所需要的信 The revolutionary breakthrough of the information network has enabled people’s living space to be squeezed by the cyberspace created by people. The completion of the global Internet so that people from the network terminal can get any information needed in time. When we enter the computer network, always hope that the more information online, the better, find out more accurate, so as to get more information. However, with the increase of network information, it is necessary to retrieve the required information