World Wide Web

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"WWW" and "The Web" redirect here. World Wide Web_sentence_0

For other uses of WWW, see WWW (disambiguation). World Wide Web_sentence_1

For uses of web, see Web (disambiguation). World Wide Web_sentence_2

For the first web software, see WorldWideWeb. World Wide Web_sentence_3

Not to be confused with the Internet. World Wide Web_sentence_4

The World Wide Web (WWW), commonly known as the Web, is an information system where documents and other web resources are identified by Uniform Resource Locators (URLs, such as https://example.com/), which may be interlinked by hypertext, and are accessible over the Internet. World Wide Web_sentence_5

The resources of the Web are transferred via the Hypertext Transfer Protocol (HTTP), may be accessed by users by a software application called a web browser, and are published by a software application called a web server. World Wide Web_sentence_6

The World Wide Web is not synonymous with the Internet, which pre-existed the Web in some form by over two decades and upon whose technologies the Web is built. World Wide Web_sentence_7

English scientist Tim Berners-Lee invented the World Wide Web in 1989. World Wide Web_sentence_8

He wrote the first web browser in 1990 while employed at CERN near Geneva, Switzerland. World Wide Web_sentence_9

The browser was released outside CERN to other research institutions starting in January 1991, and then to the general public in August 1991. World Wide Web_sentence_10

The Web began to enter everyday use in 1993-4, when websites for general use started to become available. World Wide Web_sentence_11

The World Wide Web has been central to the development of the Information Age, and is the primary tool billions of people use to interact on the Internet. World Wide Web_sentence_12

Web resources may be any type of downloaded media, but web pages are hypertext documents formatted in Hypertext Markup Language (HTML). World Wide Web_sentence_13

Special HTML syntax displays embedded hyperlinks with URLs which permits users to navigate to other web resources. World Wide Web_sentence_14

In addition to text, web pages may contain references to images, video, audio, and software components which are either displayed or internally executed in the user's web browser to render pages or streams of multimedia content. World Wide Web_sentence_15

Multiple web resources with a common theme and usually a common domain name, make up a website. World Wide Web_sentence_16

Websites are stored in computers that are running a web server, which is a program that responds to requests made over the Internet from web browsers running on a user's computer. World Wide Web_sentence_17

Website content can be provided by a publisher, or interactively from user-generated content. World Wide Web_sentence_18

Websites are provided for a myriad of informative, entertainment, commercial, and governmental reasons. World Wide Web_sentence_19

History World Wide Web_section_0

Main article: History of the World Wide Web World Wide Web_sentence_20

Tim Berners-Lee's vision of a global hyperlinked information system became a possibility by the second half of the 1980s. World Wide Web_sentence_21

By 1985, the global Internet began to proliferate in Europe and the Domain Name System (upon which the Uniform Resource Locator is built) came into being. World Wide Web_sentence_22

In 1988 the first direct IP connection between Europe and North America was made and Berners-Lee began to openly discuss the possibility of a web-like system at CERN. World Wide Web_sentence_23

While working at CERN, Berners-Lee became frustrated with the inefficiencies and difficulties posed by finding information stored on different computers. World Wide Web_sentence_24

On 12 March 1989, he submitted a memorandum, titled "Information Management: A Proposal", to the management at CERN for a system called "Mesh" that referenced ENQUIRE, a database and software project he had built in 1980, which used the term "web" and described a more elaborate information management system based on links embedded as text: "Imagine, then, the references in this document all being associated with the network address of the thing to which they referred, so that while reading this document, you could skip to them with a click of the mouse." World Wide Web_sentence_25

Such a system, he explained, could be referred to using one of the existing meanings of the word hypertext, a term that he says was coined in the 1950s. World Wide Web_sentence_26

There is no reason, the proposal continues, why such hypertext links could not encompass multimedia documents including graphics, speech and video, so that Berners-Lee goes on to use the term hypermedia. World Wide Web_sentence_27

With help from his colleague and fellow hypertext enthusiast Robert Cailliau he published a more formal proposal on 12 November 1990 to build a "Hypertext project" called "WorldWideWeb" (one word) as a "web" of "hypertext documents" to be viewed by "browsers" using a client–server architecture. World Wide Web_sentence_28

At this point HTML and HTTP had already been in development for about two months and the first Web server was about a month from completing its first successful test. World Wide Web_sentence_29

This proposal estimated that a read-only web would be developed within three months and that it would take six months to achieve "the creation of new links and new material by readers, [so that] authorship becomes universal" as well as "the automatic notification of a reader when new material of interest to him/her has become available". World Wide Web_sentence_30

While the read-only goal was met, accessible authorship of web content took longer to mature, with the wiki concept, WebDAV, blogs, Web 2.0 and RSS/Atom. World Wide Web_sentence_31

The proposal was modelled after the SGML reader Dynatext by Electronic Book Technology, a spin-off from the Institute for Research in Information and Scholarship at Brown University. World Wide Web_sentence_32

The Dynatext system, licensed by CERN, was a key player in the extension of SGML ISO 8879:1986 to Hypermedia within HyTime, but it was considered too expensive and had an inappropriate licensing policy for use in the general high energy physics community, namely a fee for each document and each document alteration. World Wide Web_sentence_33

A NeXT Computer was used by Berners-Lee as the world's first web server and also to write the first web browser in 1990. World Wide Web_sentence_34

By Christmas 1990, Berners-Lee had built all the tools necessary for a working Web: the first web browser (WorldWideWeb, which was a web editor as well) and the first web server. World Wide Web_sentence_35

The first web site, which described the project itself, was published on 20 December 1990. World Wide Web_sentence_36

The first web page may be lost, but Paul Jones of UNC-Chapel Hill in North Carolina announced in May 2013 that Berners-Lee gave him what he says is the oldest known web page during a visit to UNC in 1991. World Wide Web_sentence_37

Jones stored it on a magneto-optical drive and on his NeXT computer. World Wide Web_sentence_38

On 6 August 1991, Berners-Lee published a short summary of the World Wide Web project on the newsgroup alt.hypertext. World Wide Web_sentence_39

This date is sometimes confused with the public availability of the first web servers, which had occurred months earlier. World Wide Web_sentence_40

As another example of such confusion, several news media reported that the first photo on the Web was published by Berners-Lee in 1992, an image of the CERN house band Les Horribles Cernettes taken by Silvano de Gennaro; Gennaro has disclaimed this story, writing that media were "totally distorting our words for the sake of cheap sensationalism". World Wide Web_sentence_41

The first server outside Europe was installed in December 1991 at the Stanford Linear Accelerator Center (SLAC) in Palo Alto, California, to host the SPIRES-HEP database. World Wide Web_sentence_42

The underlying concept of hypertext originated in previous projects from the 1960s, such as the Hypertext Editing System (HES) at Brown University, Ted Nelson's Project Xanadu, and Douglas Engelbart's oN-Line System (NLS). World Wide Web_sentence_43

Both Nelson and Engelbart were in turn inspired by Vannevar Bush's microfilm-based memex, which was described in the 1945 essay "As We May Think". World Wide Web_sentence_44

Berners-Lee's breakthrough was to marry hypertext to the Internet. World Wide Web_sentence_45

In his book Weaving The Web, he explains that he had repeatedly suggested to members of both technical communities that a marriage between the two technologies was possible. World Wide Web_sentence_46

But, when no one took up his invitation, he finally assumed the project himself. World Wide Web_sentence_47

In the process, he developed three essential technologies: World Wide Web_sentence_48

World Wide Web_unordered_list_0

The World Wide Web had several differences from other hypertext systems available at the time. World Wide Web_sentence_49

The Web required only unidirectional links rather than bidirectional ones, making it possible for someone to link to another resource without action by the owner of that resource. World Wide Web_sentence_50

It also significantly reduced the difficulty of implementing web servers and browsers (in comparison to earlier systems), but in turn presented the chronic problem of link rot. World Wide Web_sentence_51

Unlike predecessors such as HyperCard, the World Wide Web was non-proprietary, making it possible to develop servers and clients independently and to add extensions without licensing restrictions. World Wide Web_sentence_52

On 30 April 1993, CERN announced that the World Wide Web would be free to anyone, with no fees due. World Wide Web_sentence_53

Coming two months after the announcement that the server implementation of the Gopher protocol was no longer free to use, this produced a rapid shift away from Gopher and toward the Web. World Wide Web_sentence_54

An early popular web browser was ViolaWWW for Unix and the X Window System. World Wide Web_sentence_55

The Web began to enter general use in 1993-4, when websites for everyday use started to become available. World Wide Web_sentence_56

Historians generally agree that a turning point for the Web began with the 1993 introduction of Mosaic, a graphical web browser developed at the National Center for Supercomputing Applications at the University of Illinois at Urbana–Champaign (NCSA-UIUC). World Wide Web_sentence_57

The development was led by Marc Andreessen, while funding came from the US High-Performance Computing and Communications Initiative and the High Performance Computing Act of 1991, one of several computing developments initiated by US Senator Al Gore. World Wide Web_sentence_58

Prior to the release of Mosaic, graphics were not commonly mixed with text in web pages, and the Web was less popular than older protocols such as Gopher and Wide Area Information Servers (WAIS). World Wide Web_sentence_59

Mosaic's graphical user interface allowed the Web to become by far the most popular protocol on the Internet. World Wide Web_sentence_60

The World Wide Web Consortium (W3C) was founded by Tim Berners-Lee after he left the European Organization for Nuclear Research (CERN) in October 1994. World Wide Web_sentence_61

It was founded at the Massachusetts Institute of Technology Laboratory for Computer Science (MIT/LCS) with support from the Defense Advanced Research Projects Agency (DARPA), which had pioneered the Internet; a year later, a second site was founded at INRIA (a French national computer research lab) with support from the European Commission DG InfSo; and in 1996, a third continental site was created in Japan at Keio University. World Wide Web_sentence_62

By the end of 1994, the total number of websites was still relatively small, but many notable websites were already active that foreshadowed or inspired today's most popular services. World Wide Web_sentence_63

Connected by the Internet, other websites were created around the world. World Wide Web_sentence_64

This motivated international standards development for protocols and formatting. World Wide Web_sentence_65

Berners-Lee continued to stay involved in guiding the development of web standards, such as the markup languages to compose web pages and he advocated his vision of a Semantic Web. World Wide Web_sentence_66

The World Wide Web enabled the spread of information over the Internet through an easy-to-use and flexible format. World Wide Web_sentence_67

It thus played an important role in popularising use of the Internet. World Wide Web_sentence_68

Although the two terms are sometimes conflated in popular use, World Wide Web is not synonymous with Internet. World Wide Web_sentence_69

The Web is an information space containing hyperlinked documents and other resources, identified by their URIs. World Wide Web_sentence_70

It is implemented as both client and server software using Internet protocols such as TCP/IP and HTTP. World Wide Web_sentence_71

Berners-Lee was knighted in 2004 by Queen Elizabeth II for "services to the global development of the Internet". World Wide Web_sentence_72

He never patented his invention. World Wide Web_sentence_73

Function World Wide Web_section_1

Main articles: HTTP and HTML World Wide Web_sentence_74

The terms Internet and World Wide Web are often used without much distinction. World Wide Web_sentence_75

However, the two terms do not mean the same thing. World Wide Web_sentence_76

The Internet is a global system of interconnected computer networks. World Wide Web_sentence_77

In contrast, the World Wide Web is a global collection of documents and other resources, linked by hyperlinks and URIs. World Wide Web_sentence_78

Web resources are accessed using HTTP or HTTPS, which are application-level Internet protocols that use the Internet's transport protocols. World Wide Web_sentence_79

Viewing a web page on the World Wide Web normally begins either by typing the URL of the page into a web browser or by following a hyperlink to that page or resource. World Wide Web_sentence_80

The web browser then initiates a series of background communication messages to fetch and display the requested page. World Wide Web_sentence_81

In the 1990s, using a browser to view web pages—and to move from one web page to another through hyperlinks—came to be known as 'browsing,' 'web surfing' (after channel surfing), or 'navigating the Web'. World Wide Web_sentence_82

Early studies of this new behaviour investigated user patterns in using web browsers. World Wide Web_sentence_83

One study, for example, found five user patterns: exploratory surfing, window surfing, evolved surfing, bounded navigation and targeted navigation. World Wide Web_sentence_84

The following example demonstrates the functioning of a web browser when accessing a page at the URL http://example.org/home.html. World Wide Web_sentence_85

The browser resolves the server name of the URL (example.org) into an Internet Protocol address using the globally distributed Domain Name System (DNS). World Wide Web_sentence_86

This lookup returns an IP address such as 203.0.113.4 or 2001:db8:2e::7334. World Wide Web_sentence_87

The browser then requests the resource by sending an HTTP request across the Internet to the computer at that address. World Wide Web_sentence_88

It requests service from a specific TCP port number that is well known for the HTTP service, so that the receiving host can distinguish an HTTP request from other network protocols it may be servicing. World Wide Web_sentence_89

HTTP normally uses port number 80 and for HTTPS it normally uses port number 443. World Wide Web_sentence_90

The content of the HTTP request can be as simple as two lines of text: World Wide Web_sentence_91

The computer receiving the HTTP request delivers it to web server software listening for requests on port 80. World Wide Web_sentence_92

If the web server can fulfil the request it sends an HTTP response back to the browser indicating success: World Wide Web_sentence_93

followed by the content of the requested page. World Wide Web_sentence_94

Hypertext Markup Language (HTML) for a basic web page might look like this: World Wide Web_sentence_95

The web browser parses the HTML and interprets the markup (<title>,

for paragraph, and such) that surrounds the words to format the text on the screen. World Wide Web_sentence_96 Many web pages use HTML to reference the URLs of other resources such as images, other embedded media, scripts that affect page behaviour, and Cascading Style Sheets that affect page layout. World Wide Web_sentence_97 The browser makes additional HTTP requests to the web server for these other Internet media types. World Wide Web_sentence_98 As it receives their content from the web server, the browser progressively renders the page onto the screen as specified by its HTML and these additional resources. World Wide Web_sentence_99

HTML World Wide Web_section_2

Main article: HTML World Wide Web_sentence_100

Hypertext Markup Language (HTML) is the standard markup language for creating web pages and web applications. World Wide Web_sentence_101

With Cascading Style Sheets (CSS) and JavaScript, it forms a triad of cornerstone technologies for the World Wide Web. World Wide Web_sentence_102

Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages. World Wide Web_sentence_103

HTML describes the structure of a web page semantically and originally included cues for the appearance of the document. World Wide Web_sentence_104

HTML elements are the building blocks of HTML pages. World Wide Web_sentence_105

With HTML constructs, images and other objects such as interactive forms may be embedded into the rendered page. World Wide Web_sentence_106

HTML provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. World Wide Web_sentence_107

HTML elements are delineated by tags, written using angle brackets. World Wide Web_sentence_108

Tags such as <img /> and <input /> directly introduce content into the page. World Wide Web_sentence_109

Other tags such as

surround and provide information about document text and may include other tags as sub-elements. World Wide Web_sentence_110 Browsers do not display the HTML tags, but use them to interpret the content of the page. World Wide Web_sentence_111 HTML can embed programs written in a scripting language such as JavaScript, which affects the behavior and content of web pages. World Wide Web_sentence_112 Inclusion of CSS defines the look and layout of content. World Wide Web_sentence_113 The World Wide Web Consortium (W3C), maintainer of both the HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997. World Wide Web_sentence_114

Linking World Wide Web_section_3

Most web pages contain hyperlinks to other related pages and perhaps to downloadable files, source documents, definitions and other web resources. World Wide Web_sentence_115

In the underlying HTML, a hyperlink looks like this: <a href="http://example.org/home.html">Example.org Homepage</a> World Wide Web_sentence_116

Such a collection of useful, related resources, interconnected via hypertext links is dubbed a web of information. World Wide Web_sentence_117

Publication on the Internet created what Tim Berners-Lee first called the WorldWideWeb (in its original CamelCase, which was subsequently discarded) in November 1990. World Wide Web_sentence_118

The hyperlink structure of the web is described by the webgraph: the nodes of the web graph correspond to the web pages (or URLs) the directed edges between them to the hyperlinks. World Wide Web_sentence_119

Over time, many web resources pointed to by hyperlinks disappear, relocate, or are replaced with different content. World Wide Web_sentence_120

This makes hyperlinks obsolete, a phenomenon referred to in some circles as link rot, and the hyperlinks affected by it are often called dead links. World Wide Web_sentence_121

The ephemeral nature of the Web has prompted many efforts to archive web sites. World Wide Web_sentence_122

The Internet Archive, active since 1996, is the best known of such efforts. World Wide Web_sentence_123

WWW prefix World Wide Web_section_4

Many hostnames used for the World Wide Web begin with www because of the long-standing practice of naming Internet hosts according to the services they provide. World Wide Web_sentence_124

The hostname of a web server is often www, in the same way that it may be ftp for an FTP server, and news or nntp for a Usenet news server. World Wide Web_sentence_125

These host names appear as Domain Name System (DNS) or subdomain names, as in www.example.com. World Wide Web_sentence_126

The use of www is not required by any technical or policy standard and many web sites do not use it; the first web server was nxoc01.cern.ch. World Wide Web_sentence_127

According to Paolo Palazzi, who worked at CERN along with Tim Berners-Lee, the popular use of www as subdomain was accidental; the World Wide Web project page was intended to be published at www.cern.ch while info.cern.ch was intended to be the CERN home page, however the DNS records were never switched, and the practice of prepending www to an institution's website domain name was subsequently copied. World Wide Web_sentence_128

Many established websites still use the prefix, or they employ other subdomain names such as www2, secure or en for special purposes. World Wide Web_sentence_129

Many such web servers are set up so that both the main domain name (e.g., example.com) and the www subdomain (e.g., www.example.com) refer to the same site; others require one form or the other, or they may map to different web sites. World Wide Web_sentence_130

The use of a subdomain name is useful for load balancing incoming web traffic by creating a CNAME record that points to a cluster of web servers. World Wide Web_sentence_131

Since, currently, only a subdomain can be used in a CNAME, the same result cannot be achieved by using the bare domain root. World Wide Web_sentence_132

When a user submits an incomplete domain name to a web browser in its address bar input field, some web browsers automatically try adding the prefix "www" to the beginning of it and possibly ".com", ".org" and ".net" at the end, depending on what might be missing. World Wide Web_sentence_133

For example, entering 'microsoft' may be transformed to http://www.microsoft.com/ and 'openoffice' to http://www.openoffice.org. World Wide Web_sentence_134

This feature started appearing in early versions of Firefox, when it still had the working title 'Firebird' in early 2003, from an earlier practice in browsers such as Lynx. World Wide Web_sentence_135

It is reported that Microsoft was granted a US patent for the same idea in 2008, but only for mobile devices. World Wide Web_sentence_136

In English, www is usually read as double-u double-u double-u. World Wide Web_sentence_137

Some users pronounce it dub-dub-dub, particularly in New Zealand. World Wide Web_sentence_138

Stephen Fry, in his "Podgrams" series of podcasts, pronounces it wuh wuh wuh. World Wide Web_sentence_139

The English writer Douglas Adams once quipped in The Independent on Sunday (1999): "The World Wide Web is the only thing I know of whose shortened form takes three times longer to say than what it's short for". World Wide Web_sentence_140

In Mandarin Chinese, World Wide Web is commonly translated via a phono-semantic matching to wàn wéi wǎng (), which satisfies www and literally means "myriad dimensional net", a translation that reflects the design concept and proliferation of the World Wide Web. World Wide Web_sentence_141

Tim Berners-Lee's web-space states that World Wide Web is officially spelled as three separate words, each capitalised, with no intervening hyphens. World Wide Web_sentence_142

Use of the www prefix has been declining, especially when Web 2.0 web applications sought to brand their domain names and make them easily pronounceable. World Wide Web_sentence_143

As the mobile Web grew in popularity, services like Gmail.com, Outlook.com, Myspace.com, Facebook.com and Twitter.com are most often mentioned without adding "www." World Wide Web_sentence_144

(or, indeed, ".com") to the domain. World Wide Web_sentence_145

Scheme specifiers World Wide Web_section_5

The scheme specifiers http:// and https:// at the start of a web URI refer to Hypertext Transfer Protocol or HTTP Secure, respectively. World Wide Web_sentence_146

They specify the communication protocol to use for the request and response. World Wide Web_sentence_147

The HTTP protocol is fundamental to the operation of the World Wide Web, and the added encryption layer in HTTPS is essential when browsers send or retrieve confidential data, such as passwords or banking information. World Wide Web_sentence_148

Web browsers usually automatically prepend http:// to user-entered URIs, if omitted. World Wide Web_sentence_149

Pages World Wide Web_section_6

Main article: Web page World Wide Web_sentence_150

A web page (also written as webpage) is a document that is suitable for the World Wide Web and web browsers. World Wide Web_sentence_151

A web browser displays a web page on a monitor or mobile device. World Wide Web_sentence_152

The term web page usually refers to what is visible, but may also refer to the contents of the itself, which is usually a containing hypertext written in HTML or a comparable markup language. World Wide Web_sentence_153

Typical web pages provide hypertext for browsing to other web pages via hyperlinks, often referred to as links. World Wide Web_sentence_154

Web browsers will frequently have to access multiple web resource elements, such as reading style sheets, scripts, and images, while presenting each web page. World Wide Web_sentence_155

On a network, a web browser can retrieve a web page from a remote web server. World Wide Web_sentence_156

The web server may restrict access to a private network such as a corporate intranet. World Wide Web_sentence_157

The web browser uses the Hypertext Transfer Protocol (HTTP) to make such requests to the web server. World Wide Web_sentence_158

A static web page is delivered exactly as stored, as web content in the web server's . World Wide Web_sentence_159

In contrast, a dynamic web page is generated by a web application, usually driven by server-side software. World Wide Web_sentence_160

Dynamic web pages are used when each user may require completely different information, for example, bank websites, web email etc. World Wide Web_sentence_161

Static page World Wide Web_section_7

Main article: Static web page World Wide Web_sentence_162

A static web page (sometimes called a flat page/stationary page) is a web page that is delivered to the user exactly as stored, in contrast to dynamic web pages which are generated by a web application. World Wide Web_sentence_163

Consequently, a static web page displays the same information for all users, from all contexts, subject to modern capabilities of a web server to negotiate content-type or language of the document where such versions are available and the server is configured to do so. World Wide Web_sentence_164

Dynamic pages World Wide Web_section_8

Main articles: Dynamic web page and Ajax (programming) World Wide Web_sentence_165

A server-side dynamic web page is a web page whose construction is controlled by an application server processing server-side scripts. World Wide Web_sentence_166

In server-side scripting, parameters determine how the assembly of every new web page proceeds, including the setting up of more client-side processing. World Wide Web_sentence_167

A client-side dynamic web page processes the web page using HTML scripting running in the browser as it loads. World Wide Web_sentence_168

JavaScript and other scripting languages determine the way the HTML in the received page is parsed into the Document Object Model, or DOM, that represents the loaded web page. World Wide Web_sentence_169

The same client-side techniques can then dynamically update or change the DOM in the same way. World Wide Web_sentence_170

A dynamic web page is then reloaded by the user or by a computer program to change some variable content. World Wide Web_sentence_171

The updating information could come from the server, or from changes made to that page's DOM. World Wide Web_sentence_172

This may or may not truncate the browsing history or create a saved version to go back to, but a dynamic web page update using Ajax technologies will neither create a page to go back to, nor truncate the web browsing history forward of the displayed page. World Wide Web_sentence_173

Using Ajax technologies the end user gets one dynamic page managed as a single page in the web browser while the actual web content rendered on that page can vary. World Wide Web_sentence_174

The Ajax engine sits only on the browser requesting parts of its DOM, the DOM, for its client, from an application server. World Wide Web_sentence_175

DHTML is the umbrella term for technologies and methods used to create web pages that are not static web pages, though it has fallen out of common use since the popularization of AJAX, a term which is now itself rarely used. World Wide Web_sentence_176

Client-side-scripting, server-side scripting, or a combination of these make for the dynamic web experience in a browser. World Wide Web_sentence_177

JavaScript is a scripting language that was initially developed in 1995 by Brendan Eich, then of Netscape, for use within web pages. World Wide Web_sentence_178

The standardised version is ECMAScript. World Wide Web_sentence_179

To make web pages more interactive, some web applications also use JavaScript techniques such as Ajax (asynchronous JavaScript and XML). World Wide Web_sentence_180

Client-side script is delivered with the page that can make additional HTTP requests to the server, either in response to user actions such as mouse movements or clicks, or based on elapsed time. World Wide Web_sentence_181

The server's responses are used to modify the current page rather than creating a new page with each response, so the server needs only to provide limited, incremental information. World Wide Web_sentence_182

Multiple Ajax requests can be handled at the same time, and users can interact with the page while data is retrieved. World Wide Web_sentence_183

Web pages may also regularly poll the server to check whether new information is available. World Wide Web_sentence_184

Website World Wide Web_section_9

Main article: Website World Wide Web_sentence_185

A website is a collection of related web resources including web pages, multimedia content, typically identified with a common domain name, and published on at least one web server. World Wide Web_sentence_186

Notable examples are wikipedia.org, google.com, and amazon.com. World Wide Web_sentence_187

A website may be accessible via a public Internet Protocol (IP) network, such as the Internet, or a private local area network (LAN), by referencing a uniform resource locator (URL) that identifies the site. World Wide Web_sentence_188

Websites can have many functions and can be used in various fashions; a website can be a personal website, a corporate website for a company, a government website, an organization website, etc. Websites are typically dedicated to a particular topic or purpose, ranging from entertainment and social networking to providing news and education. World Wide Web_sentence_189

All publicly accessible websites collectively constitute the World Wide Web, while private websites, such as a company's website for its employees, are typically a part of an intranet. World Wide Web_sentence_190

Web pages, which are the building blocks of websites, are documents, typically composed in plain text interspersed with formatting instructions of Hypertext Markup Language (HTML, XHTML). World Wide Web_sentence_191

They may incorporate elements from other websites with suitable markup anchors. World Wide Web_sentence_192

Web pages are accessed and transported with the Hypertext Transfer Protocol (HTTP), which may optionally employ encryption (HTTP Secure, HTTPS) to provide security and privacy for the user. World Wide Web_sentence_193

The user's application, often a web browser, renders the page content according to its HTML markup instructions onto a display terminal. World Wide Web_sentence_194

Hyperlinking between web pages conveys to the reader the site structure and guides the navigation of the site, which often starts with a home page containing a directory of the site web content. World Wide Web_sentence_195

Some websites require user registration or subscription to access content. World Wide Web_sentence_196

Examples of subscription websites include many business sites, news websites, academic journal websites, gaming websites, file-sharing websites, message boards, web-based email, social networking websites, websites providing real-time stock market data, as well as sites providing various other services. World Wide Web_sentence_197

End users can access websites on a range of devices, including desktop and laptop computers, tablet computers, smartphones and smart TVs. World Wide Web_sentence_198

Browser World Wide Web_section_10

Main article: Web browser World Wide Web_sentence_199

A web browser (commonly referred to as a browser) is a software user agent for accessing information on the World Wide Web. World Wide Web_sentence_200

To connect to a website's server and display its pages, a user needs to have a web browser program. World Wide Web_sentence_201

This is the program that the user runs to download, format and display a web page on the user's computer. World Wide Web_sentence_202

In addition to allowing users to find, displaying and moving between web pages, a web browser will usually have features like keeping bookmarks, recording history, managing cookies (see below) and home pages and may have facilities for recording passwords for logging into web sites. World Wide Web_sentence_203

The most popular browsers are Chrome, Firefox, Safari, Internet Explorer, and Edge. World Wide Web_sentence_204

Server World Wide Web_section_11

Main article: Web server World Wide Web_sentence_205

A Web server is server software, or hardware dedicated to running said software, that can satisfy World Wide Web client requests. World Wide Web_sentence_206

A web server can, in general, contain one or more websites. World Wide Web_sentence_207

A web server processes incoming network requests over HTTP and several other related protocols. World Wide Web_sentence_208

The primary function of a web server is to store, process and deliver web pages to clients. World Wide Web_sentence_209

The communication between client and server takes place using the Hypertext Transfer Protocol (HTTP). World Wide Web_sentence_210

Pages delivered are most frequently HTML documents, which may include images, style sheets and scripts in addition to the text content. World Wide Web_sentence_211

A user agent, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource or an error message if unable to do so. World Wide Web_sentence_212

The resource is typically a real file on the server's secondary storage, but this is not necessarily the case and depends on how the web server is implemented. World Wide Web_sentence_213

While the primary function is to serve content, a full implementation of HTTP also includes ways of receiving content from clients. World Wide Web_sentence_214

This feature is used for submitting web forms, including uploading of files. World Wide Web_sentence_215

Many generic web servers also support server-side scripting using Active Server Pages (ASP), PHP (Hypertext Preprocessor), or other scripting languages. World Wide Web_sentence_216

This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. World Wide Web_sentence_217

Usually, this function is used to generate HTML documents dynamically ("on-the-fly") as opposed to returning static documents. World Wide Web_sentence_218

The former is primarily used for retrieving or modifying information from databases. World Wide Web_sentence_219

The latter is typically much faster and more easily cached but cannot deliver dynamic content. World Wide Web_sentence_220

Web servers can also frequently be found embedded in devices such as printers, routers, webcams and serving only a local network. World Wide Web_sentence_221

The web server may then be used as a part of a system for monitoring or administering the device in question. World Wide Web_sentence_222

This usually means that no additional software has to be installed on the client computer since only a web browser is required (which now is included with most operating systems). World Wide Web_sentence_223

Cookie World Wide Web_section_12

Main article: HTTP cookie World Wide Web_sentence_224

An HTTP cookie (also called web cookie, Internet cookie, browser cookie, or simply cookie) is a small piece of data sent from a website and stored on the user's computer by the user's web browser while the user is browsing. World Wide Web_sentence_225

Cookies were designed to be a reliable mechanism for websites to remember stateful information (such as items added in the shopping cart in an online store) or to record the user's browsing activity (including clicking particular buttons, logging in, or recording which pages were visited in the past). World Wide Web_sentence_226

They can also be used to remember arbitrary pieces of information that the user previously entered into form fields such as names, addresses, passwords, and credit card numbers. World Wide Web_sentence_227

Cookies perform essential functions in the modern web. World Wide Web_sentence_228

Perhaps most importantly, authentication cookies are the most common method used by web servers to know whether the user is logged in or not, and which account they are logged in with. World Wide Web_sentence_229

Without such a mechanism, the site would not know whether to send a page containing sensitive information, or require the user to authenticate themselves by logging in. World Wide Web_sentence_230

The security of an authentication cookie generally depends on the security of the issuing website and the user's web browser, and on whether the cookie data is encrypted. World Wide Web_sentence_231

Security vulnerabilities may allow a cookie's data to be read by a hacker, used to gain access to user data, or used to gain access (with the user's credentials) to the website to which the cookie belongs (see cross-site scripting and cross-site request forgery for examples). World Wide Web_sentence_232

Tracking cookies, and especially third-party tracking cookies, are commonly used as ways to compile long-term records of individuals' browsing histories – a potential privacy concern that prompted European and U.S. lawmakers to take action in 2011. World Wide Web_sentence_233

European law requires that all websites targeting European Union member states gain "informed consent" from users before storing non-essential cookies on their device. World Wide Web_sentence_234

Google Project Zero researcher Jann Horn describes ways cookies can be read by intermediaries, like Wi-Fi hotspot providers. World Wide Web_sentence_235

He recommends to use the browser in incognito mode in such circumstances. World Wide Web_sentence_236

Search engine World Wide Web_section_13

Main article: Search engine World Wide Web_sentence_237

A web search engine or Internet search engine is a software system that is designed to carry out web search (Internet search), which means to search the World Wide Web in a systematic way for particular information specified in a web search query. World Wide Web_sentence_238

The search results are generally presented in a line of results, often referred to as search engine results pages (SERPs). World Wide Web_sentence_239

The information may be a mix of web pages, images, videos, infographics, articles, research papers and other types of files. World Wide Web_sentence_240

Some search engines also mine data available in databases or open directories. World Wide Web_sentence_241

Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler. World Wide Web_sentence_242

Internet content that is not capable of being searched by a web search engine is generally described as the deep web. World Wide Web_sentence_243

Deep web World Wide Web_section_14

Main article: Deep web World Wide Web_sentence_244

The deep web, invisible web, or hidden web are parts of the World Wide Web whose contents are not indexed by standard web search engines. World Wide Web_sentence_245

The opposite term to the deep web is the surface web, which is accessible to anyone using the Internet. World Wide Web_sentence_246

Computer scientist Michael K. Bergman is credited with coining the term deep web in 2001 as a search indexing term. World Wide Web_sentence_247

The content of the deep web is hidden behind HTTP forms, and includes many very common uses such as web mail, online banking, and services that users must pay for, and which is protected by a paywall, such as video on demand, some online magazines and newspapers, among others. World Wide Web_sentence_248

The content of the deep web can be located and accessed by a direct URL or IP address, and may require a password or other security access past the public website page. World Wide Web_sentence_249

Caching World Wide Web_section_15

A web cache is a server computer located either on the public Internet, or within an enterprise that stores recently accessed web pages to improve response time for users when the same content is requested within a certain time after the original request. World Wide Web_sentence_250

Most web browsers also implement a browser cache by writing recently obtained data to a local data storage device. World Wide Web_sentence_251

HTTP requests by a browser may ask only for data that has changed since the last access. World Wide Web_sentence_252

Web pages and resources may contain expiration information to control caching to secure sensitive data, such as in online banking, or to facilitate frequently updated sites, such as news media. World Wide Web_sentence_253

Even sites with highly dynamic content may permit basic resources to be refreshed only occasionally. World Wide Web_sentence_254

Web site designers find it worthwhile to collate resources such as CSS data and JavaScript into a few site-wide files so that they can be cached efficiently. World Wide Web_sentence_255

Enterprise firewalls often cache Web resources requested by one user for the benefit of many users. World Wide Web_sentence_256

Some search engines store cached content of frequently accessed websites. World Wide Web_sentence_257

Security World Wide Web_section_16

For criminals, the Web has become a venue to spread malware and engage in a range of cybercrimes, including (but not limited to) identity theft, fraud, espionage and intelligence gathering. World Wide Web_sentence_258

Web-based vulnerabilities now outnumber traditional computer security concerns, and as measured by Google, about one in ten web pages may contain malicious code. World Wide Web_sentence_259

Most web-based attacks take place on legitimate websites, and most, as measured by Sophos, are hosted in the United States, China and Russia. World Wide Web_sentence_260

The most common of all malware threats is SQL injection attacks against websites. World Wide Web_sentence_261

Through HTML and URIs, the Web was vulnerable to attacks like cross-site scripting (XSS) that came with the introduction of JavaScript and were exacerbated to some degree by Web 2.0 and Ajax web design that favours the use of scripts. World Wide Web_sentence_262

Today by one estimate, 70% of all websites are open to XSS attacks on their users. World Wide Web_sentence_263

Phishing is another common threat to the Web. World Wide Web_sentence_264

In February 2013, RSA (the security division of EMC) estimated the global losses from phishing at $1.5 billion in 2012. World Wide Web_sentence_265

Two of the well-known phishing methods are Covert Redirect and Open Redirect. World Wide Web_sentence_266

Proposed solutions vary. World Wide Web_sentence_267

Large security companies like McAfee already design governance and compliance suites to meet post-9/11 regulations, and some, like Finjan have recommended active real-time inspection of programming code and all content regardless of its source. World Wide Web_sentence_268

Some have argued that for enterprises to see Web security as a business opportunity rather than a cost centre, while others call for "ubiquitous, always-on digital rights management" enforced in the infrastructure to replace the hundreds of companies that secure data and networks. World Wide Web_sentence_269

Jonathan Zittrain has said users sharing responsibility for computing safety is far preferable to locking down the Internet. World Wide Web_sentence_270

Privacy World Wide Web_section_17

Main article: Internet privacy World Wide Web_sentence_271

Every time a client requests a web page, the server can identify the request's IP address. World Wide Web_sentence_272

Web servers usually log IP addresses in a . World Wide Web_sentence_273

Also, unless set not to do so, most web browsers record requested web pages in a viewable history feature, and usually cache much of the content locally. World Wide Web_sentence_274

Unless the server-browser communication uses HTTPS encryption, web requests and responses travel in plain text across the Internet and can be viewed, recorded, and cached by intermediate systems. World Wide Web_sentence_275

Another way to hide personally identifiable information is by using a virtual private network. World Wide Web_sentence_276

A VPN encrypts online traffic and masks the original IP address lowering the chance of user identification. World Wide Web_sentence_277

When a web page asks for, and the user supplies, personally identifiable information—such as their real name, address, e-mail address, etc. web-based entities can associate current web traffic with that individual. World Wide Web_sentence_278

If the website uses HTTP cookies, username, and password authentication, or other tracking techniques, it can relate other web visits, before and after, to the identifiable information provided. World Wide Web_sentence_279

In this way, it is possible for a web-based organization to develop and build a profile of the individual people who use its site or sites. World Wide Web_sentence_280

It may be able to build a record for an individual that includes information about their leisure activities, their shopping interests, their profession, and other aspects of their . World Wide Web_sentence_281

These profiles are obviously of potential interest to marketers, advertisers, and others. World Wide Web_sentence_282

Depending on the website's terms and conditions and the local laws that apply information from these profiles may be sold, shared, or passed to other organizations without the user being informed. World Wide Web_sentence_283

For many ordinary people, this means little more than some unexpected e-mails in their in-box or some uncannily relevant advertising on a future web page. World Wide Web_sentence_284

For others, it can mean that time spent indulging an unusual interest can result in a deluge of further targeted marketing that may be unwelcome. World Wide Web_sentence_285

Law enforcement, counter-terrorism, and espionage agencies can also identify, target, and track individuals based on their interests or proclivities on the Web. World Wide Web_sentence_286

Social networking sites usually try to get users to use their real names, interests, and locations, rather than pseudonyms, as their executives believe that this makes the social networking experience more engaging for users. World Wide Web_sentence_287

On the other hand, uploaded photographs or unguarded statements can be identified to an individual, who may regret this exposure. World Wide Web_sentence_288

Employers, schools, parents, and other relatives may be influenced by aspects of social networking profiles, such as text posts or digital photos, that the posting individual did not intend for these audiences. World Wide Web_sentence_289

Online bullies may make use of personal information to harass or stalk users. World Wide Web_sentence_290

Modern social networking websites allow fine-grained control of the privacy settings for each individual posting, but these can be complex and not easy to find or use, especially for beginners. World Wide Web_sentence_291

Photographs and videos posted onto websites have caused particular problems, as they can add a person's face to an on-line profile. World Wide Web_sentence_292

With modern and potential facial recognition technology, it may then be possible to relate that face with other, previously anonymous, images, events and scenarios that have been imaged elsewhere. World Wide Web_sentence_293

Due to image caching, mirroring, and copying, it is difficult to remove an image from the World Wide Web. World Wide Web_sentence_294

Standards World Wide Web_section_18

Main article: Web standards World Wide Web_sentence_295

Web standards include many interdependent standards and specifications, some of which govern aspects of the Internet, not just the World Wide Web. World Wide Web_sentence_296

Even when not web-focused, such standards directly or indirectly affect the development and administration of web sites and web services. World Wide Web_sentence_297

Considerations include the interoperability, accessibility and usability of web pages and web sites. World Wide Web_sentence_298

Web standards, in the broader sense, consist of the following: World Wide Web_sentence_299

World Wide Web_unordered_list_1

Web standards are not fixed sets of rules, but are a constantly evolving set of finalized technical specifications of web technologies. World Wide Web_sentence_300

Web standards are developed by standards organizations—groups of interested and often competing parties chartered with the task of standardization—not technologies developed and declared to be a standard by a single individual or company. World Wide Web_sentence_301

It is crucial to distinguish those specifications that are under development from the ones that already reached the final development status (in case of W3C specifications, the highest maturity level). World Wide Web_sentence_302

Accessibility World Wide Web_section_19

Main article: Web accessibility World Wide Web_sentence_303

There are methods for accessing the Web in alternative mediums and formats to facilitate use by individuals with disabilities. World Wide Web_sentence_304

These disabilities may be visual, auditory, physical, speech-related, cognitive, neurological, or some combination. World Wide Web_sentence_305

Accessibility features also help people with temporary disabilities, like a broken arm, or ageing users as their abilities change. World Wide Web_sentence_306

The Web receives information as well as providing information and interacting with society. World Wide Web_sentence_307

The World Wide Web Consortium claims that it is essential that the Web be accessible, so it can provide equal access and equal opportunity to people with disabilities. World Wide Web_sentence_308

Tim Berners-Lee once noted, "The power of the Web is in its universality. World Wide Web_sentence_309

Access by everyone regardless of disability is an essential aspect." World Wide Web_sentence_310

Many countries regulate web accessibility as a requirement for websites. World Wide Web_sentence_311

International co-operation in the W3C Web Accessibility Initiative led to simple guidelines that web content authors as well as software developers can use to make the Web accessible to persons who may or may not be using assistive technology. World Wide Web_sentence_312

Internationalisation World Wide Web_section_20

The W3C Internationalisation Activity assures that web technology works in all languages, scripts, and cultures. World Wide Web_sentence_313

Beginning in 2004 or 2005, Unicode gained ground and eventually in December 2007 surpassed both ASCII and Western European as the Web's most frequently used character encoding. World Wide Web_sentence_314

Originally RFC  allowed resources to be identified by URI in a subset of US-ASCII. World Wide Web_sentence_315

RFC  allows more characters—any character in the Universal Character Set—and now a resource can be identified by IRI in any language. World Wide Web_sentence_316

See also World Wide Web_section_21

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/World Wide Web.