Search Engine

 A web search engine is designed to search for information on the World Wide Web and FTP servers. The search results are generally presented in a list of results and are often called hits. The information may consist of web pages, images, information and other types of files. Some search engines also mine data available in databases or open directories. Unlike Web directories, which are maintained by human editors, search engines operate algorithmically or are a mixture of algorithmic and human input.

Timeline
Year	Engine	Event
1993	W3Catalog	Launch
	Aliweb	Launch
	JumpStation	Launch
1994	WebCrawler	Launch
	Go.com	Launch
	Lycos	Launch
1995	AltaVista	Launch
	Daum	Founded
	Open Text Web Index	Launch
	Magellan	Launch
	Excite	Launch
	SAPO	Launch
	Yahoo!	Launch
1996	Dogpile	Launch
	Inktomi	Closed (is not Yahoo!)
	HotBot	Founded
	Ask Jeeves	Founded
1997	Northern Light	Launch
	Yandex	Launch
1998	Google	Launch
1999	AlltheWeb	Launch
	GenieKnows	Founded
	Naver	Launch
	Teoma	Founded
	Vivisimo	Founded
2000	Baidu	Founded
	Exalead	Founded
2003	Info.com	Launch
2004	Yahoo! Search	Final launch
	A9.com	Closed
	Sogou	Launch
2005	MSN Search	Closed (is Bing now)
	Ask.com	Launch
	GoodSearch	Launch
	SearchMe	Founded
2006	wikiseek	Founded
	Quaero	Founded
	Ask.com	Launch
	Live Search	Closed (is now Bing)
	ChaCha	Launch
	Guruji.com	Launch
2007	wikiseek	Closed
	Sproose	Closed
	Wikia Search	Launched
	Blackle.com	Launched
2008	Powerset	Closed (Became Bing)
	Picollator	Closed
	Viewzi	Closed
	Cuil	Launched
	Boogami	Launched
	LeapFish	Beta Launch
	Forestle	Launched
	VADLO	Launched
	Duck Duck Go	Launched
2009	Bing	Launched
	Yebol	Beta Launch
	Mugurdy	Closed due to a lack of funding
	Goby	Launched
2010	Yandex global (English)	Launched
	Cuil	Closed
	Blekko	Beta Launch
	Viewzi	Closed due to a lack of funding

How web search engines work

A search engine operates, in the following order

1. Web crawling
2. Indexing
3. Searching

Web search engines work by storing information about many web pages, which they retrieve from the html itself. These pages are retrieved by a Web crawler (sometimes also known as a spider) — an automated Web browser which follows every link on the site. Exclusions can be made by the use of robots.txt. The contents of each page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). Data about web pages are stored in an index database for use in later queries. A query can be a single word. The purpose of an index is to allow information to be found as quickly as possible. 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, whereas others, 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, so it can be very useful when the content of the current page has been updated and the search terms are no longer in it. This problem might be considered to be a mild form of linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be on the returned webpage. This satisfies the principle of least astonishment since the user normally expects the search terms to be on the returned pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available elsewhere.
When a user enters a query into a search engine (typically by using key words), the engine examines its index and provides a listing of best-matching web pages according to its criteria, usually with a short summary containing the document's title and sometimes parts of the text. The index is built from the information stored with the data and the method by which the information is indexed. Unfortunately, there are currently no known public search engines that allow documents to be searched by date. Most search engines support the use of the boolean operators AND, OR and NOT to further specify the search query. Boolean operators are for literal searches that allow the user to refine and extend the terms of the search. The engine looks for the words or phrases exactly as entered. Some search engines provide an advanced feature called proximity search which allows users to define the distance between keywords. There is also concept-based searching where the research involves using statistical analysis on pages containing the words or phrases you search for. As well, natural language queries allow the user to type a question in the same form one would ask it to a human. A site like this would be ask.com.
The usefulness of a search engine depends on the relevance of the result set it gives back. While there may be millions of web pages that include a particular word or phrase, some pages may be more relevant, popular, or authoritative than others. Most search engines employ methods to rank the results to provide the "best" results first. How a search engine decides which pages are the best matches, and what order the results should be shown in, varies widely from one engine to another. The methods also change over time as Internet usage changes and new techniques evolve. There are two main types of search engine that have evolved: one is a system of predefined and hierarchically ordered keywords that humans have programmed extensively. The other is a system that generates an "inverted index" by analyzing texts it locates. This second form relies much more heavily on the computer itself to do the bulk of the work.
Most Web search engines are commercial ventures supported by advertising revenue and, as a result, some employ the practice of allowing advertisers to pay money to have their listings ranked higher in search results. Those search engines which do not accept money for their search engine results make money by running search related ads alongside the regular search engine results. The search engines make money every time someone clicks on one of these ads.

Market share and wars

According to Net Marketshare. In December 2010, rankings the market share of web search engine, showed Google is 84.65%, Yahoo is 6.69%, Baidu is 3.39%, Bing is 3.29% and other is 1.98%.The Google's worldwide market share peaked at 86.3% in April, 2010.
In the United States, Google held a 63.2% market share in May 2009, according to Nielsen NetRatings.
In the People's Republic of China, Baidu held a 61.6% market share for web search in July 2009.

Search engine bias

Although search engines are programmed to rank websites based on their popularity and relevancy, empirical studies indicate various political, economic, and social biases in the information they provide.These biases could be a direct result of economic and commercial processes (e.g., companies that advertise with a search engine can become also more popular in its organic search results), and political processes (e.g., the removal of search results in order to comply with local laws).Google Bombing is one example of an attempt to manipulate search results for political, social or commercial reasons.

Source: www.wikipedia.org