| An Internet search engine is a software program specially-designed to search for data on the World Wide Web. The search results are usually provided in the form of a list and are normally called hits. The information may include web pages, images, information and other types of files. Some search engines also collect data available in databanks or open directories. If compared to Internet directories which are maintained by human editors, search engines work algorithmically or are a mix of human and algorithmic input.
Web search engines work by storing data about countless 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 sees. The content of each page is then analyzed to determine how it should be indexed. Words, for instance, are extracted 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 tools, such as Google, save and store the entire or part of the source page (also called a cache) as well as data about web pages, whereas others, such as AltaVista, save and store every word of every page they have discovered. The cached page always comprises the initial search text, because it is the one that was actually indexed. Thus, it can be very helpful since it includes information that may no longer be found anywhere else on the Web.
When a user types key words in the search field, the software program carries out checks on its databank and shows a listing of best-matching web pages in accordance with its parameters, commonly with a brief summary containing the document's title and sometimes extracts from the text. Some search tools have introduced an advanced tool called proximity search which allows users to define the length between key words.
The usefulness of a search engine depends on the relevancy of the results it provides. Since there may be millions of web pages containing a particular word or phrase, web pages can be divided into relevant and irrelevant ones. The majority of search engines apply methods to rank the results to display the "best" results first.
How a search engine decides which pages are the best matches, and in what order the results should be displayed, is specific to a search engine. The methods also change in time, as the use of Internet services alters and new techniques are developed. |
