Wiki

Some wikis have an edit button or link directly on the page being viewed if the user has permission to edit the page. This can lead to a text-based editing page where participants can structure and format wiki pages with a simplified markup language, sometimes known as wikitext, wiki markup or wikicode (it can also lead to a WYSIWYG editing page; see the paragraph after the table below). For example, starting lines of text with asterisks could create a bulleted list. The style and syntax of wikitexts can vary greatly among wiki implementations, some of which also allow HTML tags.

Wikis have favored plain-text editing, with fewer and simpler conventions than HTML for indicating style and structure. Although limiting access to HTML and Cascading Style Sheets (CSS) of wikis limits user ability to alter the structure and formatting of wiki content, there are some benefits. Limited access to CSS promotes consistency in the look and feel, and having JavaScript disabled prevents a user from implementing code that may limit other users' access.

Wikis can also make WYSIWYG editing available to users, usually through a JavaScript control that translates graphically entered formatting instructions into the corresponding HTML tags or wikitext. In those implementations, the markup of a newly edited, marked-up version of the page is generated and submitted to the server transparently, shielding the user from this technical detail. An example of this is the VisualEditor on Wikipedia. WYSIWYG controls do not, however, always provide all the features available in wikitext, and some users prefer not to use a WYSIWYG editor. Hence, many of these sites offer some means to edit the wikitext directly.

Some wikis keep a record of changes made to wiki pages; often, every version of the page is stored. This means that authors can revert to an older version of the page should it be necessary because a mistake has been made, such as the content accidentally being deleted or the page has been vandalized to include offensive or malicious text or other inappropriate content.

Many wiki implementations, such as MediaWiki, the software that powers Wikipedia, allow users to supply an edit summary when they edit a page. This is a short piece of text summarizing the changes they have made (e.g. "Corrected grammar" or "Fixed formatting in table"). It is not inserted into the article's main text but is stored along with that revision of the page, allowing users to explain what has been done and why. This is similar to a log message when making changes in a revision-control system. This enables other users to see which changes have been made by whom and why, often in a list of summaries, dates and other short, relevant content, a list which is called a "log" or "history".

Within the text of most pages, there are usually many hypertext links to other pages within the wiki. This form of non-linear navigation is more "native" to a wiki than structured/formalized navigation schemes. Users can also create any number of index or table-of-contents pages, with hierarchical categorization or whatever form of organization they like. These may be challenging to maintain "by hand", as multiple authors and users may create and delete pages in an ad hoc, unorganized manner. Wikis can provide one or more ways to categorize or tag pages to support the maintenance of such index pages. Some wikis, including the original, have a backlink feature, which displays all pages that link to a given page. It is also typically possible in a wiki to create links to pages that do not yet exist, as a way to invite others to share what they know about a subject new to the wiki. Wiki users can typically "tag" pages with categories or keywords, to make it easier for other users to find the article. For example, a user creating a new article on cold-weather biking might "tag" this page under the categories of commuting, winter sports and bicycling. This would make it easier for other users to find the article.

Links are created using a specific syntax, the so-called "link pattern". Originally, most wikis used CamelCase to name pages and create links. These are produced by capitalizing words in a phrase and removing the spaces between them (the word "CamelCase" is itself an example). While CamelCase makes linking easy, it also leads to links in a form that deviates from the standard spelling. To link to a page with a single-word title, one must abnormally capitalize one of the letters in the word (e.g. "WiKi" instead of "Wiki"). CamelCase-based wikis are instantly recognizable because they have many links with names such as "TableOfContents" and "BeginnerQuestions". A wiki can render the visible anchor of such links "pretty" by reinserting spaces, and possibly also reverting to lower case. This reprocessing of the link to improve the readability of the anchor is, however, limited by the loss of capitalization information caused by CamelCase reversal. For example, "RichardWagner" should be rendered as "Richard Wagner", whereas "PopularMusic" should be rendered as "popular music". There is no easy way to determine which capital letters should remain capitalized. As a result, many wikis now have "free linking" using brackets, and some disable CamelCase by default.

Most wikis offer at least a title search, and sometimes a full-text search. The scalability of the search depends on whether the wiki engine uses a database. Some wikis, such as PmWiki, use flat files.[12] MediaWiki's first versions used flat files, but it was rewritten by Lee Daniel Crocker in the early 2000s (decade) to be a database application. Indexed database access is necessary for high speed searches on large wikis. Alternatively, external search engines such as Google Search can sometimes be used on wikis with limited searching functions to obtain more precise results.

History comparison reports highlight the changes between two revisions of a page.

Wikis are generally designed with the philosophy of making it easy to correct mistakes, rather than making it difficult to make them. Thus, while wikis are very open, they provide a means to verify the validity of recent additions to the body of pages. The most prominent, on almost every wiki, is the "Recent Changes" page—a specific list showing recent edits, or a list of edits made within a given time frame.[21] Some wikis can filter the list to remove minor edits and edits made by automatic importing scripts ("bots").[22] From the change log, other functions are accessible in most wikis: the revision history shows previous page versions and the diff feature highlights the changes between two revisions. Using the revision history, an editor can view and restore a previous version of the article. This gives great power to the author to eliminate edits. The diff feature can be used to decide whether or not this is necessary. A regular wiki user can view the diff of an edit listed on the "Recent Changes" page and, if it is an unacceptable edit, consult the history, restoring a previous revision; this process is more or less streamlined, depending on the wiki software used.[23]

In case unacceptable edits are missed on the "recent changes" page, some wiki engines provide additional content control. It can be monitored to ensure that a page, or a set of pages, keeps its quality. A person willing to maintain pages will be warned of modifications to the pages, allowing them to verify the validity of new editions quickly. This can be seen as a very pro-author and anti-editor feature.[24] A watchlist is a common implementation of this. Some wikis also implement "patrolled revisions", in which editors with the requisite credentials can mark some edits as not vandalism. A "flagged revisions" system can prevent edits from going live until they have been reviewed.[25]

Critics of publicly editable wiki systems argue that these systems could be easily tampered with by malicious individuals ("vandals") or even by well-meaning but unskilled users who introduce errors into the content, while proponents maintain that the community of users can catch such malicious or erroneous content and correct it.[2] Lars Aronsson, a data systems specialist, summarizes the controversy as follows: "Most people when they first learn about the wiki concept, assume that a Web site that can be edited by anybody would soon be rendered useless by destructive input. It sounds like offering free spray cans next to a grey concrete wall. The only likely outcome would be ugly graffiti and simple tagging and many artistic efforts would not be long lived. Still, it seems to work very well."[13] High editorial standards in medicine and health sciences articles, in which users typically use peer-reviewed journals or university textbooks as sources, have led to the idea of expert-moderated wikis.[26] Some wikis allow one to link to specific versions of articles, which has been useful to the scientific community, in that expert peer reviewers could analyse articles, improve them and provide links to the trusted version of that article.[27] Noveck points out that "participants are accredited by members of the wiki community, who have a vested interest in preserving the quality of the work product, on the basis of their ongoing participation." On controversial topics that have been subject to disruptive editing, a wiki author may restrict editing to registered users.[28]

The open philosophy of wiki – allowing anyone to edit content – does not ensure that every editor's intentions are well-mannered. For example, vandalism (changing wiki content to something offensive, adding nonsense, maliciously removing content, or deliberately adding incorrect information, such as hoax information) can be a major problem. On larger wiki sites, such as those run by the Wikimedia Foundation, vandalism can go unnoticed for some period of time. Wikis, because of their open nature, are susceptible to intentional disruption, known as "trolling". Wikis tend to take a soft-security approach to the problem of vandalism, making damage easy to undo rather than attempting to prevent damage. Larger wikis often employ sophisticated methods, such as bots that automatically identify and revert vandalism and JavaScript enhancements that show characters that have been added in each edit. In this way, vandalism can be limited to just "minor vandalism" or "sneaky vandalism", where the characters added/eliminated are so few that bots do not identify them and users do not pay much attention to them.[29] An example of a bot that reverts vandalism on Wikipedia is ClueBot NG. ClueBot NG can revert edits, often within minutes, if not seconds. The bot uses machine learning in lieu of heuristics.[30]

The amount of vandalism a wiki receives depends on how open the wiki is. For instance, some wikis allow unregistered users, identified by their IP addresses, to edit content, while others limit this function to just registered users.[31]

Edit wars can also occur as users repetitively revert a page to the version they favor. In some cases, editors with opposing views of which content should appear or what formatting style should be used will change and re-change each other's edits. This results in the page being "unstable" from a general user's perspective, because each time a general user comes to the page, it may look different. Some wiki software allows an administrator to stop such edit wars by locking a page from further editing until a decision has been made on what version of the page would be most appropriate.[10] Some wikis are in a better position than others to control behavior due to governance structures existing outside the wiki. For instance, a college teacher can create incentives for students to behave themselves on a class wiki they administer by limiting editing to logged-in users and pointing out that all contributions can be traced back to the contributors. Bad behavior can then be dealt with under university policies.[12]

Malware can also be a problem for wikis, as users can add links to sites hosting malicious code. For example, a German Wikipedia article about the Blaster Worm was edited to include a hyperlink to a malicious website. Users of vulnerable Microsoft Windows systems who followed the link would be infected.[10] A countermeasure is the use of software that prevents users from saving an edit that contains a link to a site listed on a blacklist of malicious sites.

The home page of the English Wikipedia

The English Wikipedia has the largest user base among wikis on the World Wide Web[32] and ranks in the top 10 among all Web sites in terms of traffic.[33] Other large wikis include the WikiWikiWeb, Memory Alpha, Wikivoyage, and previously Susning.nu, a Swedish-language knowledge base. Medical and health-related wiki examples include Ganfyd, an online collaborative medical reference that is edited by medical professionals and invited non-medical experts.[11] Many wiki communities are private, particularly within enterprises. They are often used as internal documentation for in-house systems and applications. Some companies use wikis to allow customers to help produce software documentation.[34] A study of corporate wiki users found that they could be divided into "synthesizers" and "adders" of content. Synthesizers' frequency of contribution was affected more by their impact on other wiki users, while adders' contribution frequency was affected more by being able to accomplish their immediate work.[35] From a study of thousands of wiki deployments, Jonathan Grudin concluded careful stakeholder analysis and education are crucial to successful wiki deployment.[36]

In 2005, the Gartner Group, noting the increasing popularity of wikis, estimated that they would become mainstream collaboration tools in at least 50% of companies by 2009.[37] Wikis can be used for project management.[38][39] Wikis have also been used in the academic community for sharing and dissemination of information across institutional and international boundaries.[40] In those settings, they have been found useful for collaboration on grant writing, strategic planning, departmental documentation, and committee work.[41] In the mid-2000s, the increasing trend among industries toward collaboration placed a heavier impetus upon educators to make students proficient in collaborative work, inspiring even greater interest in wikis being used in the classroom.[10]

Wikis have found some use within the legal profession and within the government. Examples include the Central Intelligence Agency's Intellipedia, designed to share and collect intelligence, DKospedia, which was used by the American Civil Liberties Union to assist with review of documents about the internment of detainees in Guantánamo Bay;[42] and the wiki of the United States Court of Appeals for the Seventh Circuit, used to post court rules and allow practitioners to comment and ask questions. The United States Patent and Trademark Office operates Peer-to-Patent, a wiki to allow the public to collaborate on finding prior art relevant to the examination of pending patent applications. Queens, New York has used a wiki to allow citizens to collaborate on the design and planning of a local park. Cornell Law School founded a wiki-based legal dictionary called Wex, whose growth has been hampered by restrictions on who can edit.[28]

In academic contexts, wikis have also been used as project collaboration and research support systems.[43][44]

A city wiki (or local wiki) is a wiki used as a knowledge base and social network for a specific geographical locale.[45][46][47] The term 'city wiki' or its foreign language equivalent (e.g. German 'Stadtwiki') is sometimes also used for wikis that cover not just a city, but a small town or an entire region. A city wiki contains information about specific instances of things, ideas, people and places. Much of this information might not be appropriate for encyclopedias such as Wikipedia (e.g. articles on every retail outlet in a town), but might be appropriate for a wiki with more localized content and viewers. A city wiki could also contain information about the following subjects, that may or may not be appropriate for a general knowledge wiki, such as:

• Details of public establishments such as public houses, bars, accommodation or social centers
• Owner name, opening hours and statistics for a specific shop
• Statistical information about a specific road in a city
• Flavors of ice cream served at a local ice cream parlor
• A biography of a local mayor and other persons

WikiNodes are pages on wikis that describe related wikis. They are usually organized as neighbors and delegates. A neighbor wiki is simply a wiki that may discuss similar content or may otherwise be of interest. A delegate wiki is a wiki that agrees to have certain content delegated to that wiki.[48] One way of finding a wiki on a specific subject is to follow the wiki-node network from wiki to wiki.

The four basic types of users who participate in wikis are reader, author, wiki administrator and system administrator. The system administrator is responsible for the installation and maintenance of the wiki engine and the container web server. The wiki administrator maintains wiki content and is provided additional functions about pages (e.g. page protection and deletion), and can adjust users' access rights by, for instance, blocking them from editing.[49]

A study of several hundred wikis showed that a relatively high number of administrators for a given content size is likely to reduce growth;[50] that access controls restricting editing to registered users tends to reduce growth; that a lack of such access controls tends to fuel new user registration; and that higher administration ratios (i.e. admins/user) have no significant effect on content or population growth.[51]