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4.4 BASIS FOR RANKINGS

Human-powered search engines, like Yahoo, index all listings by humans. They index and rank web pagesby the knowledge and experience they have. With automatic engines indexing happens with crawler. They try to find the most important information that describe web pages, and they have to rank them somehow. Thebasic ranking methods for relevant information are the same in automatical crawler-based search engines, likeGoogle and Altavista. They notice information location on web pages, the title and first paragraphs usually contain relevant keywords. Another main ranking method in search engines is keywords frequency in web page. Although every major search engine use that location/frequency method, but it still can be distinguished many differencies between them. Nobody does it exactly the same, which is one reason why the same search on different search engines produces different results To begin with, some search engines index more web pages than others. Some search engines also index web pages more often than others, for example indexing happens in Altavista in one or two days while it takes much longer in Google. The result is that no search engine has the exact same collection of web pages to search through. Search engines may also give web pages a rank boost for certain reasons. There are several different features that search engines uses as a ranking boost so every search engine has their own combination to measure web pages’ information relevancy. The following table describes the main ranking boost methods between major search engines. Link popularity is one of them. It tells which of the pages in its index have a lot of links pointing at them, so it uses the connection between popularity and relevancy. Some search engines support the meta description and keywords tag that give pages an extra boost if search terms appear in these areas. Some search engines also review sites or list them in an associated directory. They may also give a boost to sites that have been listed in that way. Direct Hit is a system that measures what users click on from search results. It defines the relevancy from users’ point of view.

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