Because of the depth and breadth of information being indexed, there is usually a delay, sometimes up to several weeks, between the time a site has been“spidered”and when it appears in a search index.Until this two-step process has been completed, a site remains unavailable to search queries.
Finally, the heart of each search engine is an algorithm that matches keyword queries against the information in the index, ranking results in the order the algorithm deems most relevant.
Because the spiders, resulting indexes, and search algorithms of each search engine differ, so do the search results and rankings across the various search engines.This explains why a top 10 site in HotBot may not appear near the top of Alta Vista when the same keyword search criterion is entered.
In addition, many, but not all, search utilities also reference metatags—invisible HTML tags within documents that describe their content—as a way to control how content is indexed.As a result, proper use of metatags throughout a site can also boost search engine ranking.
因特网搜索工具分为两大阵营：搜索引擎，如HotBot和AltaVista，以及在线目录，如 Yahoo和Lycos。两者间的差别与它们如何编撰网站编目有关。当然，对任何规律都有例外。有些搜索实用程序，如Ask Jeeves，把搜索引擎和目录方法合并成单一的软件包，希望把这两个阵营中最好的东西提供给用户。