A search engine is a special kind of website. It has a Web address like any other website, but its job is to help you find other websites on the Internet. 

Like a card catalogue of subjects, authors, and titles in a library, a search engine is a huge index of words used to find websites. It attempts to include each word from every page of the entire WWW in its databases. 

But due to the enormous quantity of Web pages, this is impossible to achieve. In 1997, even the biggest search engine (which was AltaVista at the time) was able to cover only 60% to 70% of the Web in its database. Research, from the NEC Research Institute in 1999, has shown that the eleven top search engines together only cover about 42% of the Web, or 335 million pages.  It seems fair to say that the search engines manage to cover only a tiny section of the Web. Nonetheless, they remain the best tools to help us find 'direct' information from the Web by using search techniques.

Search engines make use of "robots", "spiders", "crawlers", and various other computer programmes to trace hyperlinks across the Web. As these "robots" cruise from one site to the next, they index, or catalogue, web documents and send the results back to a database. When you introduce a search term, the "robot" checks its database and presents the results in a list. 

If a search engine finds a document with the information that you're looking for, it will show you the link to that document on the screen. We call this a "hit". Because there is so much information available on the Internet, these results may amount to several thousand so-called "hits". You normally only look at the first 20 or 30 hits in the list.

adapted from: http://cwis.kub.nl/~dbi/english/instruct/www/7uk.htm

If you ask a search engine to look for information, this is what it does:

• It takes the information you give it, word-by-word; and
• Compares it with what it has in its database; and then
• Gives you the result in the form of a list of websites.

Each website in the list is linked to information. All you do is click on these links to read more and find the information you require.

Different search engines use different approaches. In this module, we focus on several basic approaches:

Natural language search - using AskJeeves

Subject searching, also known as an information index - using Yahoo

Keyword searching - using Google

Keyword searching using Alta Vista (optional)

You may explore these links now, but we will introduce them to you one-by-one during this course.