A search engine usually refers to searching for information on the Web. Other kinds of the search engine are enterprise search engines, which search on intranets, personal search engines, and mobile search engines. Different selection and relevance criteria may apply in different environments, or for different uses.
Web search engines operate in the following order: 1) Web crawling, 2) Indexing, 3) Searching. Search engines store information about a large number of web pages, which they look up in the Web itself. These pages are retrieved by a Web crawler (sometimes also known as a spider). It is
an automated Web browser which follows every link it sees. The contents of each page are then analyzed to determine how it should be indexed. Data about web pages are stored in an index database. Some search engines, such as Google, store all or part of the source page (referred to as a cache) as well as information about the web pages. Other engines, such as AltaVista, store every word of every page they find. This cached page always holds the actual search text since it is the one that was actually indexed. Search engines use regularly updated indexes to operate quickly and efficiently.
When a user makes a query, commonly by giving key words, the search engine looks up the index and provides a listing of best-matching web pages according to its criteria. Usually the listing comprises a short summary containing the document title and sometimes parts of the text. Most search engines support the use of the Boolean terms AND, OR and NOT to further specify the search query. The listing is often sorted with respect to some measure of relevance of the results. An advanced feature is proximity search, which allows users to define the distance between key words.
Most Web search engines are commercial ventures supported by advertising revenue. As a result, some of the engines employ the controversial practice of allowing advertisers to pay money to have their listings ranked higher in search outcomes. The vast majority of search engines running by private companies use proprietary algorithms and closed databases, though a few of them are open sources.
Nowadays the most popular search engines are as follows:
Google. Around 2001, the Google search engine rose to prominence. Its success was based in part on the concept of link popularity and PageRank. Further it utilizes more than 150 criteria to determine relevancy. Google is currently the most of all used search engine.
Baidu. Due to the difference between Ideographic and Alphabet writing system, the Chinese search market didn’t boom until the introduction of Baidu in 2000. Since then, neither Google, Yahoo nor Microsoft could come to the top like in other part of the world. The reason may be the media control policy of the Chinese government, which requires any network media to filter any possible sensitive information out from their web pages.
Yahoo! Search. Only since 2004, Yahoo! Search has become an original web crawler-based search engine, with a reinvented crawler called Yahoo! Slurp. Its new search engine results were included in all of Yahoo! sites that had a web search function. It also started to sell its search engine results to other companies, to show on their web sites.
After the boom success of key word search engines, such as Google and Yahoo! search, a new type of a search engine, a meta search engine, appears. In general, the meta search engine is not a search engine. Technically, it is a search engine based on search engines. A typical meta search engine accepts user queries the same as that of traditional search engines. But instead of searching key words in its own database, it sends those queries to other non-meta search engines. Then based on the search results returned by several non-meta search engines, it selects the best ones (according on different algorithms), showing back to users. Examples of those meta search engines are Dog Pile (http://www.dogpile.com/) and All in One News (http://www.allinonenews.com/ – About Allinonenews).
PS: The text is drawn up within an upcoming e-book titled Internet English (see Number 33 – WWW, Part 1 / August 2011 – Editorial). G. Vitkova
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