4  The WWW and search engines

• When you try to find a web page using a search engine, the search engine looks through the index of the pages created by the web crawler.
• The search engine will examine the search term and compare it against the index of information it holds for:
  • how often the search words occur on a page
  • where they are on a page
  • if they occur together
  • if there are similar words.
• It uses this information to choose web pages that it considers to best meet your search request. The pages are then displayed in order, with the ones meeting the search term best being shown at the top.
• Some search engines (e.g. Google) use the concept of rank when presenting search results. This considers the amount of links on other relevant websites pointing towards a particular page. The more links from related web pages, the higher the ranking.
• Search engines accept payments from commercial organisations to place their web pages higher up the displayed list from a given search, even if their page is not a particularly good match.
• This is a form of advertising, and the search result will be marked with ‘Ad’ to indicate this:

Figure 7

• To learn more, take a look at the following videos:
  • Matt Cutts’s video on ‘How Search Works’.

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  • Google’s video, ‘Verbatim and double quotes’, on search terms.