Web 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. 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 ofrobots.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. Some examples of Search engines:- 1.ask.com(known as Ask Jeeves in the UK) 2.Baidu (Chinese, Japanese) 3.Bing (formerly MSN Search and Live Search) 4.Duck Duck Go 5.Google 6.Kosmix 7.Sogou (Chinese) 8.Yodao (Chinese) 9.Yahoo! Search 10.Yandex (Russian) 11.Yebol www.ask.com It is a search engine which is founded in 1996,whose headquarter is in Oakland,California,US. The name of founder of ask.com is David warthen and garrett Gruener. The original search engine software was implemented by Gary Chevsky from his own design. Chevsky, Justin Grant, and others built the early AskJeeves.com website around that core engine. Three venture capital firms, Highland Capital Partners, Institutional Venture Partners, and The RODA Group were early investors.[2] Ask.com is currently owne d by InterActiveCorp under the NASDAQ symbol IACI . History:- Ask.com was originally known as Ask Jeeves, where "Jeeves" is the name of the "gentleman's personal gentleman", or valet, fetching answers to any question asked. The character was based on Jeeves, Bertie Wooster's fictional valet from the works of P. G. Wodehouse. The original idea behind Ask Jeeves was to allow users to get answers to questions posed in everyday, natural language, as well as traditional keyword searching. The current Ask.com still supports this, with added support for math, dictionary, and conversion questions. In 2005, the company announced plans to phase out Jeeves. On February 27, 2006, the character disappeared from Ask.com, and was stated to be "going in to retirement." The UK & Ireland edition of the website prominently brought the character back in 2009, however American visitors can go to the 'uk.ask.com' URL to see the new Jeeves as a 'skin', or background image. InterActiveCorp owns a variety of sites including country-specific sites for UK, Germany, Italy,Japan, the Netherlands, and Spain along with Ask Kids, Teoma (now ExpertRank) and several others (see this page for a complete list). On June 5, 2007 Ask.com relaunched with a 3D look. On May 16, 2006, Ask implemented a "Binoculars Site Preview" into its search results. On search results pages, the "Binoculars" let searchers capture a sneak peak of the page they could visit with a mouse- over activating screenshot pop-up. In December 2007, Ask released the AskEraser feature, allowing users to opt-out from tracking of search queries and IP and cookie values. They also vowed to erase this data after 18 months if the AskEraser option is not set. HTTP cookies must be enabled for AskEraser to function. On July 4, 2008 InterActiveCorp announced the acquisition of Lexico Publishing Group, which owns Dictionary.com, Thesaurus.com, and Reference.com. On July 26th 2010, Ask.com released a closed-beta Q&A service. The service was released to the public on July 29th 2010. Toolbar The Ask.com Toolbar is a free internet browser toolbar from Ask.com, available for both the Internet Explorer and Firefox web browsers. The toolbar is frequently confused with the MyWay Searchbar, however the Ask Toolbar and the MyWay Searchbar are separate programs. Features include the web, image, news, dictionary searches, a wide variety of US and international content served in widgets, weather forecasts, RSS/ATOM feeds and related services. The Ask Toolbar can be installed from the toolbar.ask.com website, but is also bundled with certain 3rd party software. The installation of the Ask Toolbar is optional to the user and always requires end user consent (in the form of an "Opt-Out" check box) when bundled with other 3rd party software. The Ask.com toolbar has been reported by some to contain spyware or adware, and has also been reported by some to be a virus (though it is not, it is simply a potentially unwanted program).[20] The program itself however, could be considered adware, because it is bundled as an ad to certain software installations. Dekker’s algorithm of Ask.com Dekker's algorithm is the first known correct solution to the mutual exclusion problem in concurrent programming. The solution is attributed to Dutch mathematician Th. J. Dekker by Edsger W. Dijkstrain his manuscript on cooperating sequential processes[1]. It allows two threads to share a single-use resource without conflict, using only shared memory for communication. It avoids the strict alternation of a naive turn-taking algorithm, and was one of the first mutual exclusion algorithms to be invented Pseudocode flag[0] := false flag[1] := false turn := 0 // or 1 p0: p1: flag[0] := true flag[1] := true while flag[1] = true { while flag[0] = true { if turn ≠ 0 { if turn ≠ 1 { flag[0] := false flag[1] := false while turn ≠ 0 { while turn ≠ 1 { } } flag[0] := true flag[1] := true } } } } // critical section // critical section ..