Starting at the top level with the major categories, users search down through the category tree. Typically pages listed on a Directory search engine are pre-screened. Yahoo is the best example of this type of service. Index Servers Index search engines are simply a giant index of words linked to web pages.
Users enter keywords to do a search.
Hotbot and AltaVista are good examples of this type of search engine. Combination Servers Several servers now provide both keyword index searches and a directory search capacity. It is sometimes difficult to know if the keyword searchs look in only their directory tree or in a general web index. Lycos and Excite are good examples of this type of search engine. Meta Servers Meta servers will search using other seach engines.