| A web search engine is a software programme designed to search for information on the Web. The search results are usually provided in the form of a list and are usually called hits. The information may consist of web pages, images, information and other types of files. Some search engines also collect data available in databanks or open directories. Unlike Web directories which are maintained by human editors, search tools work automatically or are a mix of human and algorithmic input.
Internet search engines function by storing information about numerous web pages which they retrieve from the WWW. These pages are retrieved by a web crawler, also known as a spider. It is an automatically-controlled Web browser which follows every link it discovers. Afterwards the content of each page is analyzed to determine how to index it. Words, for instance, are removed from titles, headings and subheadings or special fields called meta tags. Data about web pages are stored in an index database for further use in queries. Some search engines, such as Google, store the whole or part of the source page (referred to as a cache) and information about web pages, while others, such as AltaVista, store every word of every page they have discovered. This cached page always contains the initial search text, as it is the one that was actually indexed. Hence, it can be very useful because it comprises data that can no longer be found anywhere else on the Web.
Once a web user has typed search words in the search field, the engine looks through its index and shows a list of the most suitable web pages in accordance with its criteria, commonly with a brief summary coupled with the document's title and sometimes extracts from the text. Some search tools have introduced an advanced feature called proximity search which allows users to determine the length between search words.
The relevancy of the results determines the usefulness of a search engine. Since there can be millions of web pages that comprise a particular word or word combination, some pages may be more relevant and popular than others. The results can be ranked to display the "best" ones first.
The way a search software programme ranks web pages differs from one engine to another. The methods also change in time, since the use of the Internet undergoes alterations and new techniques become available. |
