Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation. Its name is a portmanteau of the words wiki (a technology for creating collaborative websites, from the Hawaiian word wiki, meaning "quick") and encyclopedia. Wikipedia's 15 million articles (3.2 million in English) have been written collaboratively by volunteers around the world, and almost all of its articles can be edited by anyone with access to the site. It was launched in 2001 by Jimmy Wales and Larry Sanger and is currently the largest and most popular general reference work on the Internet. Its reliability and accuracy are also targeted. Other criticisms center on its susceptibility to vandalism and the addition of spurious or unverified information, and an investigation in Nature found that the material they compared came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors". Some noted the importance of Wikipedia not only as an encyclopedic reference but also as a frequently updated news resource because of how quickly articles about recent events appear.

History

thumb|right|alt=Logo reading "Nupedia.com the free encyclopedia" in blue with large initial "N".|Wikipedia originally developed from another encyclopedia project, , Wikipedia (January 21, 2007) was codified in its initial months, and was similar to Nupedia's earlier "nonbiased" policy. Otherwise, there were relatively few rules initially and Wikipedia operated independently of Nupedia.  have been started to address perceived limitations of Wikipedia, such as its policies on peer review, original research, and commercial advertising.thumb|right|Number of articles in the English Wikipedia plotted against In November 2009, a Ph.D thesis written by Felipe Ortega, a researcher at the Universidad Rey Juan Carlos in Madrid, found that the English Wikipedia had lost 49,000 editors during the first three months of 2009; in comparison, the project lost only 4,900 editors during the same period in 2008. The finding was disputed by Jimmy Wales, who denied the decline and questioned the methodology of the study.

Nature of Wikipedia

Editing model

thumb|In April 2009, the In departure from the style of traditional encyclopedias, Wikipedia consistently employs the open editing model called "wiki". Except for a few vandalism-prone pages that can be edited only by established users, or in extreme cases only by administrators, every article may be edited anonymously or with a user account, while only registered users may create a new article (only in English edition). No article is owned by its creator or any other editor, or is vetted by any recognized authority; rather, the articles are collectively owned by a community of editors.Most importantly, when changes to an article are made, they become available immediately before undergoing any review, no matter if they contain an error, are somehow misguided, or even patent nonsense. The German edition of Wikipedia is an exception to this rule: it has been testing a system of maintaining "stable versions" of articles, to allow a reader to see versions of articles that have passed certain reviews. The English edition of Wikipedia plans to trial a related approach. Another proposal is the use of software to create "trust ratings" for individual Wikipedia contributors and using those ratings to determine which changes will be made visible immediately.thumb|left|alt=Web page showing side-by-side comparison of an article highlighting changed paragraphs.| Researcher Giacomo Poderi found that articles tend to reach the FA status via intensive works of few editors. In 2007, in preparation for producing a print version, the English-language Wikipedia introduced an assessment scale against which the quality of articles is judged; other editions have also adopted this.A WikiProject is a place for a group of editors to coordinate works on a specific topic. The discussion pages attached to a project are often used to coordinate changes that take place across articles. Wikipedia also maintains a style guide called the Manual of Style or MoS for short, which stipulates, for example, cases in which an article must start with the article title in bold in the first sentence.In 2008, two researchers theorized that the growth of Wikipedia is sustainable.

Defenses against undesirable edits

The open nature of the editing model has been central to most criticism of Wikipedia. For example, a reader of an article cannot be certain that it has not been compromised by the insertion of false information or the removal of essential information. Former Encyclopædia Britannica editor-in-chief Robert McHenry once described this by saying:thumb|alt=White-haired elderly gentleman in suit and tie speaks at a podium.| In practice, obvious vandalism is fairly easy to remove from wikis, and the median time to detect and fix vandalisms is typically very low, usually a few minutes, John Seigenthaler, the founding editorial director of USA Today and founder of the Freedom Forum First Amendment Center at Vanderbilt University, called Jimmy Wales and asked if Wales had any way of knowing who contributed the misinformation. Wales replied that he did not. This incident led to policy changes on the site, specifically targeted at tightening up the verifiability of all biographical articles of living people.Wikipedia's open structure inherently makes it an easy target for Internet trolls, spamming, and those with an agenda to push. The addition of political spin to articles by organizations including members of the U.S. House of Representatives and special interest groups has been noted, and organizations such as Microsoft have offered financial incentives to work on certain articles. These issues have been parodied, notably by Stephen Colbert in The Colbert Report.For example, in August 2007, the website WikiScanner began to trace the sources of changes made to Wikipedia by anonymous editors without Wikipedia accounts. The program revealed that many such edits were made by corporations or government agencies changing the content of articles related to them, their personnel or their work.

Community

The Wikipedia community has established "a bureaucracy of sorts", including "a clear power structure that gives volunteer administrators the authority to exercise editorial control."Wikipedia's community has also been described as "cult-like", although not always with entirely negative connotations, and criticized for failing to accommodate inexperienced users.thumb|right| , Kuro5hin, December 31, 2004.In a 2003 study of Wikipedia as a community, economics Ph.D. student Andrea Ciffolilli argued that the low transaction costs of participating in wiki software create a catalyst for collaborative development, and that a "creative construction" approach encourages participation. In his 2008 book, The Future of the Internet and How to Stop It, Jonathan Zittrain of the Oxford Internet Institute and Harvard Law Schools Berkman Center for Internet & Society cites Wikipedia's success as a case study in how open collaboration has fostered innovation on the web. A 2008 study found that Wikipedia users were less agreeable and open, though more conscientious, than non-Wikipedia users. A 2009 study suggested there was "evidence of growing resistance from the Wikipedia community to new content." At OOPSLA 2009, Wikimedia CTO and Senior Software Architect gave a presentation entitled "Community Performance Optimization: Making Your People Run as Smoothly as Your Site" in which he discussed the challenges of handling the contributions from a large community and compared the process to that of software development.The Wikipedia Signpost is the community newspaper on the English Wikipedia, and was founded by Michael Snow, an administrator and the current chair of the Wikimedia Foundation board of trustees. It covers news and events from the site, as well as major events from sister projects, such as Wikimedia Commons.Notable users of Wikipedia include film critic Roger Ebert and University of Maryland physicist Robert L. Park. In 2009, the Wall Street Journal reported that "unprecedented numbers of the millions of online volunteers who write, edit and police are quitting." The array of rules applied to editing and disputes related to such content are among the reasons for this trend that are cited in the article.

Operation

Wikimedia Foundation and the Wikimedia chapters

Wikipedia is hosted and funded by the Wikimedia Foundation, a non-profit organization which also operates Wikipedia-related projects such as Wiktionary and Wikibooks. The Wikimedia chapters, local associations of users and supporters of the Wikimedia projects, also participate in the promotion, the development, and the funding of the project.

Software and hardware

The operation of Wikipedia depends on MediaWiki, a custom-made, free and open source wiki software platform written in PHP and built upon the MySQL database. The software incorporates programming features such as a macro language, variables, a transclusion system for templates, and URL redirection. MediaWiki is licensed under the GNU General Public License and used by all Wikimedia projects, as well as many other wiki projects. Originally, Wikipedia ran on UseModWiki written in Perl by Clifford Adams (Phase I), which initially required CamelCase for article hyperlinks; the present double bracket style was incorporated later. Starting in January 2002 (Phase II), Wikipedia began running on a PHP wiki engine with a MySQL database; this software was custom-made for Wikipedia by Magnus Manske. The Phase II software was repeatedly modified to accommodate the exponentially increasing demand. In July 2002 (Phase III), Wikipedia shifted to the third-generation software, MediaWiki, originally written by Lee Daniel Crocker.Several MediaWiki extensions are installed to extend the functionality of MediaWiki software.In April 2005 a Lucene extension was added to MediaWiki's built-in search and Wikipedia switched from MySQL to Lucene for searching. Currently Lucene Search 2.1, which is written in Java and based on Lucene library 2.3, is used.meta:Server layout diagrams|server layout diagrams on Meta-Wiki.Wikipedia currently runs on dedicated clusters of Linux servers (mainly Ubuntu), with a few OpenSolaris machines for ZFS. As of December 2009, there were 300 in Florida and 44 in Amsterdam. Wikipedia employed a single server until 2004, when the server setup was expanded into a distributed multitier architecture. In January 2005, the project ran on 39 dedicated servers in Florida. This configuration included a single master database server running MySQL, multiple slave database servers, 21 web servers running the Apache HTTP Server, and seven Squid cache servers.Wikipedia receives between 25,000 and 60,000 page requests per second, depending on time of day. Page requests are first passed to a front-end layer of Squid caching servers. Further statistics are available based on a publicly-available 3-months Wikipedia access trace. Requests that cannot be served from the Squid cache are sent to load-balancing servers running the Linux Virtual Server software, which in turn pass the request to one of the Apache web servers for page rendering from the database. The web servers deliver pages as requested, performing page rendering for all the language editions of Wikipedia. To increase speed further, rendered pages are cached in a distributed memory cache until invalidated, allowing page rendering to be skipped entirely for most common page accesses. Two larger clusters in the Netherlands and Korea now handle much of Wikipedia's traffic load.

Delivery media

Wikipedia's original medium was for users to read and edit content using any standard web browser through a fixed internet connection. However, Wikipedia content is now also accessible through offline media, and through the mobile web.On mobile devices access to Wikipedia from mobile phones was possible as early as 2004, through the Wireless Application Protocol (WAP), through the Wapedia service. In June 2007, Wikipedia launched , an official website for wireless devices. In 2009 a newer mobile service was officially released, located at , which caters to more advanced mobile devices such as the iPhone, Android-based devices, or the Palm Pre. Several other methods of mobile access to Wikipedia have emerged (See ). Several devices and applications optimise or enhance the display of Wikipedia content for mobile devices, while some also incorporate additional features such as use of Wikipedia metadata (See ), such as geoinformation.Collections of Wikipedia articles have been published on optical disks. An English version, 2006 Wikipedia CD Selection, contained about 2,000 articles. The Polish version contains nearly 240,000 articles. There are also German versions.

License and language editions

All text in Wikipedia was covered by GNU Free Documentation License (GFDL), a copyleft license permitting the redistribution, creation of derivative works, and commercial use of content while authors retain copyright of their work, up until June 2009, when the site switched to Creative Commons Attribution-ShareAlike (CC-by-SA) 3.0. Wikipedia had been working on the switch to Creative Commons licenses because the GFDL, initially designed for software manuals, is not suitable for online reference works and because the two licenses were incompatible. In response to the Wikimedia Foundation's request, in November 2008, the Free Software Foundation (FSF) released a new version of GFDL designed specifically to allow Wikipedia to by August 1, 2009. Wikipedia and its sister projects held a community-wide referendum to decide whether or not to make the license switch. The referendum took place from April 9 to 30. The results were 75.8% "Yes", 10.5% "No", and 13.7% "No opinion". In consequence of the referendum, the Wikimedia Board of Trustees voted to change to the Creative Commons license, effective June 15, 2009.thumb|right|Percentage of all Wikipedia articles in English and top ten largest language editions . As of July 2007, less than 23% of Wikipedia articles are in English.The handling of media files (e.g., image files) varies across language editions. Some language editions, such as the English Wikipedia, include non-free image files under fair use doctrine, while the others have opted not to. This is in part because of the difference in copyright laws between countries; for example, the notion of fair use does not exist in Japanese copyright law. Media files covered by free content licenses (e.g., Creative Commons' cc-by-sa) are shared across language editions via Wikimedia Commons repository, a project operated by the Wikimedia Foundation.There are currently 262 language editions of Wikipedia; of these, 24 have over 100,000 articles and 81 have over 1,000 articles. According to Alexa, the English subdomain (en.wikipedia.org; English Wikipedia) receives approximately 54% of Wikipedia's cumulative traffic, with the remaining split among the other languages (Japanese: 10%, German: 8%, Spanish: 5%, Russian: 4%, French: 4%, Italian: 3%).Since Wikipedia is web-based and therefore worldwide, contributors of a same language edition may use different dialects or may come from different countries (as is the case for the English edition). These differences may lead to some conflicts over spelling differences, (e.g. color vs. colour) or points of view.Though the various language editions are held to global policies such as "neutral point of view," they diverge on some points of policy and practice, most notably on whether images that are not licensed freely may be used under a claim of fair use. USA 52.1, UK 15.9, Canada 7.3, Austria 4.4, Germany 1.8, Netherlands 1.6, France 1, Others 15.8.|Contributors for English Wikipedia by country as of September 2006.Jimmy Wales has described Wikipedia as "an effort to create and distribute a free encyclopedia of the highest possible quality to every single person on the planet in their own language". Though each language edition functions more or less independently, some efforts are made to supervise them all. They are coordinated in part by Meta-Wiki, the Wikimedia Foundation's wiki devoted to maintaining all of its projects (Wikipedia and others). For instance, Meta-Wiki provides important statistics on all language editions of Wikipedia, and it maintains a list of articles every Wikipedia should have. The list concerns basic content by subject: biography, history, geography, society, culture, science, technology, foodstuffs, and mathematics. As for the rest, it is not rare for articles strongly related to a particular language not to have counterparts in another edition. For example, articles about small towns in the United States might only be available in English.Translated articles represent only a small portion of articles in most editions, in part because automated translation of articles is disallowed. Articles available in more than one language may offer "InterWiki" links, which link to the counterpart articles in other editions.

Cultural significance

"You suck!"|Wikipedia shown in , LEGISINFO (March 28, 2005) The encyclopedia's assertions are increasingly used as a source by organizations such as the U.S. Federal Courts and the World Intellectual Property Organization  though mainly for supporting information rather than information decisive to a case. Content appearing on Wikipedia has also been cited as a source and referenced in some U.S. intelligence agency reports. In December 2008, the scientific journal RNA Biology launched a new section for descriptions of families of RNA molecules and requires authors who contribute to the section to also submit a draft article on the RNA family for publication in Wikipedia.thumb|alt=The Onion newspaper front page.| ", San Antonio Express-News, January 9, 2007.In July 2007, Wikipedia was the focus of a 30-minute documentary on BBC Radio 4 which argued that, with increased usage and awareness, the number of references to Wikipedia in popular culture is such that the term is one of a select band of 21st-century nouns that are so familiar (Google, Facebook, YouTube) that they no longer need explanation and are on a par with such 20th-century terms as Hoovering or Coca-Cola. Many parody Wikipedia's openness, with characters vandalizing or modifying the online encyclopedia project's articles. Notably, comedian Stephen Colbert has parodied or referenced Wikipedia on numerous episodes of his show The Colbert Report and coined the related term "wikiality". Others draw upon Wikipedia's motto, such as in "The Negotiation," an episode of The Office, where character Michael Scott says "Wikipedia is the best thing ever. Anyone in the world can write anything they want about any subject, so you know you are getting the best possible information". More rarely, Wikipedia's internal policies are parodied, such as in the xkcd strip "Wikipedian Protester."

thumb|left|alt=Simple line drawing of man speaking at podium; one member of a large crowd holds up a sign saying "citation needed".|An

On September 28, 2007, Italian politician Franco Grillini raised a parliamentary question with the Minister of Cultural Resources and Activities about the necessity of freedom of panorama. He said that the lack of such freedom forced Wikipedia, "the seventh most consulted website" to forbid all images of modern Italian buildings and art, and claimed this was hugely damaging to tourist revenues.

thumb| On September 16, 2007, The Washington Post reported that Wikipedia had become a focal point in the 2008 U.S. election campaign, saying, "Type a candidate's name into Google, and among the first results is a Wikipedia page, making those entries arguably as important as any ad in defining a candidate. Already, the presidential entries are being edited, dissected and debated countless times each day." An October 2007 Reuters article, titled "Wikipedia page the latest status symbol", reported the recent phenomenon of how having a Wikipedia article vindicates one's notability.

Wikipedia won two major awards in May 2004. The first was a Golden Nica for Digital Communities of the annual Prix Ars Electronica contest; this came with a 10,000 (£6,588; $12,700) grant and an invitation to present at the PAE Cyberarts Festival in Austria later that year. The second was a Judges' Webby Award for the "community" category. Wikipedia was also nominated for a "Best Practices" Webby. On January 26, 2007, Wikipedia was also awarded the fourth highest brand ranking by the readers of brandchannel.com, receiving 15% of the votes in answer to the question "Which brand had the most impact on our lives in 2006"

In September 2008, Wikipedia received Quadriga A Mission of Enlightenment award of Werkstatt Deutschland along with Boris Tadi, Eckart Höfling, and Peter Gabriel. The award was presented to Jimmy Wales by David Weinberger.

In July 2009, BBC Radio 4 broadcast a comedy series called Bigipedia, which was set on a website which was a parody of Wikipedia. Some of the sketches were directly inspired by Wikipedia and its articles.

Related projects

A number of interactive multimedia encyclopedias incorporating entries written by the public existed long before Wikipedia was founded. The first of these was the 1986 BBC Domesday Project, which included text (entered on BBC Micro computers) and photographs from over 1 million contributors in the UK, and covering the geography, art, and culture of the UK. This was the first interactive multimedia encyclopedia (and was also the first major multimedia document connected through internal links), with the majority of articles being accessible through an interactive map of the UK. The user-interface and part of the content of the Domesday Project were emulated on a website until 2008. One of the most successful early online encyclopedias incorporating entries by the public was h2g2, which was created by Douglas Adams and is run by the BBC. The h2g2 encyclopedia was relatively light-hearted, focusing on articles which were both witty and informative. Both of these projects had similarities with Wikipedia, but neither gave full editorial freedom to public users. A similar non-wiki project, the GNUPedia project, co-existed with Nupedia early in its history; however, it has been retired and its creator, free software figure Richard Stallman, has lent his support to Wikipedia. created in October 2002, detailed the September 11 attacks; this project was closed in October 2006. Wiktionary, a dictionary project, was launched in December 2002; Wikiquote, a collection of quotations, a week after Wikimedia launched, and Wikibooks, a collection of collaboratively written free textbooks and annotated texts. Wikimedia has since started a number of other projects, including Wikiversity, a project for the creation of free learning materials and the provision of online learning activities. None of these sister projects, however, has come to meet the success of Wikipedia.

Some subsets of Wikipedia's information have been developed, often with additional review for specific purposes.For example, Wikipedia for Schools, the Wikipedia series of CDs/DVDs, produced by Wikipedians and SOS Children, is a free, hand-checked, non-commercial selection from Wikipedia targeted around the UK National Curriculum and intended to be useful for much of the English speaking world. The project is available online; an equivalent print encyclopedia would require roughly 20 volumes. There has also been an attempt to put a select subset of Wikipedia's articles into printed book form.

Other websites centered on collaborative knowledge base development have drawn inspiration from or inspired Wikipedia. Some, such as Susning.nu, Enciclopedia Libre, Hudong, Baidu Baike, and WikiZnanie likewise employ no formal review process, whereas others use more traditional peer review, such as Encyclopedia of Life, Stanford Encyclopedia of Philosophy, Scholarpedia, h2g2, and Everything2. The online wiki-based encyclopedia Citizendium was started by Wikipedia co-founder Larry Sanger in an attempt to create an "expert-friendly" Wikipedia.