______搜索引擎没有自己数据，当用户输入检索关键词时，将用户请求同时向多个搜索引擎提交，并将返回结果进行重复排除、重新排序等处理后，作为自己结果返回给用户。
- A.元
- B.目录
- C.蜘蛛
- D.机器人
正确答案及解析
正确答案
解析
本题考查搜索引擎分类基本概念。按照信息搜集方法不同，搜索引擎系统可以分为三类：①目录式搜索引擎(Directory Search Engine)该类搜索引擎以人工或半自动方式搜集信息，由编辑员查看信息之后，人工形成信息摘要，并将信息置于事先确定分类框架中。信息大多面向网站，提供目录浏览服务和直接检索服务。这种搜索引擎因为加入了人智能，所以信息准确、导航质量高，缺点是需要人工介入(维护工作量大)、信息量少、信息更新不及时。目录式搜索引擎代表是：Yahoo!、LookSmart、Ask Jeeves、Snap、Open Directory.②机器人搜索引擎(Crawler-Based Search Engine)该类搜索引擎由一个称为蜘蛛(Spider)机器人程序以某种策略自动地在Internet中搜集和发现信息，由索引器为搜集到信息建立索引，由检索器根据用户查询输入检索索引库，并将查询结果返回给用户。服务方式是面向网页全文检索服务。该类搜索引擎具有信息量大、更新及时、毋需人工干预特点，但不可避免地引发了大量冗余信息，用户必须手动进行筛选。机器人搜索引擎代表是：AltaVista、Northern Light，Excite、Infoseek、Inktomi.FAST、Lycos、Google.③元搜索引擎(Meta Search Engine)该类搜索引擎没有自己数据，当用户输入检索关键词时，它将用户请求同时向多个搜索引擎递交，将返回结果进行重复排除、重新排序等处理后，作为自己结果返回给用户。服务方式为面向网页全文检索。这类搜索引擎同样具有返回结果信息量大特点，缺点与机器人搜索引擎相同。元搜索引擎代表是WebCrawler、InfoMarket。
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