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When you enter a search string, such as the words 'computer shopper magazine website', your search engine will look in its database for sites containing those words. Enter this search string into Google, and the search engine will find over one million matching websites. If these were presented to you in no particular order, you might never find the real Computer Shopper website. To get around this problem, search engines try to assess the relevance of each page they find, and present the most relevant ones to you first. Another big difference between search engines is how they decide which of the pages that match your search string are the most important.

The criteria by which a search engine determines which pages to present first vary. Some engines look at where, and how often, the words in your search string appear in the document. Increasingly, search engines are following Google's example and assigning each site a 'rank'. This rank is calculated mainly by looking at how many other, unrelated pages link to that page. The more inbound links there are, the more authoritative the search engine assumes the page to be, and the higher the rank it gives it; see the 'Rank and file' box on page 126 for a fuller explanation of Google PageRank. When you search, the engine displays the pages that match your search criteria from highest to lowest.

As we will explain, there are plenty of ways in which you can help search engines to even greater precision, reducing the number of irrelevant entries and increasing the chance that the exact information you want will be on one of the pages close to the top of your list of search results.

In the past few years, search engines have appeared that don't have their own

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database of websites matched to keywords, such as Dogpile (www.dogpile.com). Instead, these types of search engines transmit your search request to a number of other search sites, allowing you to use several search engines simultaneously. These are called meta search engines.

Simple searches

Once you know how a search engine works, you're a step closer to being able to find exactly the results you want in less time. However, before we look at advanced search tips, it's worth going over the basics.

First, think about how the information you are looking for might be described by someone who knows the topic well. You should try and avoid, or at least qualify, words or search strings that may have double meanings. For instance, if you're looking for the internationally recognised and definitive rules of football, the search string 'football rules' might not be specific enough. You may simply find fan sites written by people who think football is fantastic. However, if you used the string 'FIFA laws of the game' you'll get what you want first time.

If you find that a search string is returning only one or two pages that contain relevant information, don't give up. Browse those pages for alternative words or phrases that might be of more use. Similarly, try using synonyms. So if you can't find what you need searching for "advantages clean fuel" try "benefits clean fuel". Where appropriate, you should try both British and American spellings, though some search engines (notably Google) are smart enough to search both spellings simultaneously.

Advanced search tools

One of the easiest ways to make your search more precise is to use the advanced search tools that are provided by most search engines. These allow you to narrow your search according to several common criteria, such as language, date, format (HTML, PDF and so on) and where in the site the words in your search string should appear (URL, title, body text and so on). Advanced search tools generally allow you to specify whether you want to search for the exact phrase you entered, or all the words but in no particular order, or at least one of the words, and so on. You can usually find a link to a site's advanced search tool somewhere at the top of the page near the search box itself.