Hyperlink

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An example of a hyperlink as commonly seen in a web browser, with a mouse pointer hovering above it Hyperlink-Wikipedia.svg
An example of a hyperlink as commonly seen in a web browser, with a mouse pointer hovering above it
Several documents being connected by hyperlinks Sistema hipertextual.jpg
Several documents being connected by hyperlinks

In computing, a hyperlink, or simply a link, is a reference to data that the user can follow by clicking or tapping. [1] A hyperlink points to a whole document or to a specific element within a document. Hypertext is text with hyperlinks. The text that is linked from is called anchor text. A software system that is used for viewing and creating hypertext is a hypertext system, and to create a hyperlink is to hyperlink (or simply to link). A user following hyperlinks is said to navigate or browse the hypertext.

Contents

The document containing a hyperlink is known as its source document. For example, in an online reference work such as Wikipedia, or Google, many words and terms in the text are hyperlinked to definitions of those terms. Hyperlinks are often used to implement reference mechanisms such as tables of contents, footnotes, bibliographies, indexes, letters and glossaries.

In some hypertext, hyperlinks can be bidirectional: they can be followed in two directions, so both ends act as anchors and as targets. More complex arrangements exist, such as many-to-many links.

The effect of following a hyperlink may vary with the hypertext system and may sometimes depend on the link itself; for instance, on the World Wide Web most hyperlinks cause the target document to replace the document being displayed, but some are marked to cause the target document to open in a new window (or, perhaps, in a new tab). [2] Another possibility is transclusion, for which the link target is a document fragment that replaces the link anchor within the source document. Not only persons browsing the document follow hyperlinks. These hyperlinks may also be followed automatically by programs. A program that traverses the hypertext, following each hyperlink and gathering all the retrieved documents is known as a Web spider or crawler.

An inline link displays remote content without the need for embedding the content. The remote content may be accessed with or without the user following the link.

An inline link may display a modified version of the content; for instance, instead of an image, a thumbnail, low resolution preview, cropped section, or magnified section may be shown. The full content is then usually available on demand, as is the case with print publishing software  e.g., with an external link. This allows for smaller file sizes and quicker response to changes when the full linked content is not needed, as is the case when rearranging a page layout.

Anchor

An anchor hyperlink is a link bound to a portion of a document [3]   generally text, though not necessarily. For instance, it may also be a hot area in an image (image map in HTML), a designated, often irregular part of an image. One way to define it is by a list of coordinates that indicate its boundaries. For example, a political map of Africa may have each country hyperlinked to further information about that country. A separate invisible hot area interface allows for swapping skins or labels within the linked hot areas without repetitive embedding of links in the various skin elements.

A fat link (also known as a "one-to-many" link, an "extended link" [4] or a "multi-tailed link") [5] is a hyperlink which leads to multiple endpoints; the link is a multivalued function.

Uses in various technologies

HTML

Tim Berners-Lee saw the possibility of using hyperlinks to link any information to any other information over the Internet. Hyperlinks were therefore integral to the creation of the World Wide Web. Web pages are written in the hypertext mark-up language HTML.

This is what a hyperlink to the home page of the W3C organization could look like in HTML code:

<ahref="https://www.w3.org/">W3C organization website</a>

This HTML code consists of several tags:

Webgraph is a graph, formed from web pages as vertices and hyperlinks, as directed edges.

The W3C Recommendation called XLink describes hyperlinks that offer a far greater degree of functionality than those offered in HTML. These extended links can be multidirectional, linking from, within, and between XML documents. It can also describe simple links, which are unidirectional and therefore offer no more functionality than hyperlinks in HTML.

Wikis

While wikis may use HTML-type hyperlinks, the use of wiki markup, a set of lightweight markup languages specifically for wikis, provides a simplified syntax for linking pages within wiki environments  in other words, for creating wikilinks.

How internal MediaWiki links work when one wants to create a link that displays words different from the linked page's title. Wiki-linking.png
How internal MediaWiki links work when one wants to create a link that displays words different from the linked page's title.

The syntax and appearance of wikilinks may vary. Ward Cunningham's original wiki software, the WikiWikiWeb used CamelCase for this purpose. CamelCase was also used in the early version of Wikipedia and is still used in some wikis, such as TiddlyWiki, Trac, and PmWiki. A common markup syntax is the use of double square brackets around the term to be wikilinked. For example, the input "[[zebras]]" is converted by wiki software using this markup syntax to a link to a zebras article. Hyperlinks used in wikis are commonly classified as follows:

Wikilinks are visibly distinct from other text, and if an internal wikilink leads to a page that does not yet exist, it usually has a different specific visual appearance. For example, in Wikipedia wikilinks are displayed in blue, except those that link to pages that don't yet exist, which are instead shown in red. [6] Another possibility for linking is to display a highlighted clickable question mark after the wikilinked term.

Virtual worlds

Hyperlinks are being implemented in various 3D virtual world networks, including those that use the OpenSimulator [7] and Open Cobalt [8] platforms.

Permalinks are URLs that are intended to remain unchanged for many years into the future, yielding hyperlink that are less susceptible to link rot. Permalinks are often rendered simply, that is, as friendly URLs, so as to be easy for people to type and remember. Permalinks are used in order to point and redirect readers to the same Web page, blog post or any online digital media. [9]

The scientific literature is a place where link persistence is crucial to the public knowledge. A 2013 study in BMC Bioinformatics analyzed 15,000 links in abstracts from Thomson Reuters’ Web of Science citation index, founding that the median lifespan of Web pages was 9.3 years, and just 62% were archived. [10] The median lifespan of a Web page constitutes high-degree variable, but its order of magnitude usually is of some months. [11]

A link from one domain to another is said to be outbound from its source anchor and inbound to its target.

The most common destination anchor is a URL used in the World Wide Web. This can refer to a document, e.g. a webpage, or other resource, or to a position in a webpage. The latter is achieved by means of an HTML element with a "name" or "id" attribute at that position of the HTML document. The URL of the position is the URL of the webpage with a fragment identifier   "#id attribute"  appended.

When linking to PDF documents from an HTML page the "id attribute" can be replaced with syntax that references a page number or another element of the PDF, for example, "#page=386".

A web browser usually displays a hyperlink in some distinguishing way, e.g. in a different color, font or style, or with certain symbols following to visualize link target or document types. This is also called link decoration. The behavior and style of links can be specified using the Cascading Style Sheets (CSS) language.

In a graphical user interface, the appearance of a mouse cursor may change into a hand motif to indicate a link. In most graphical web browsers, links are displayed in underlined blue text when they have not been visited, but underlined purple text when they have. When the user activates the link (e.g., by clicking on it with the mouse) the browser displays the link's target. If the target is not an HTML file, depending on the file type and on the browser and its plugins, another program may be activated to open the file.

The HTML code contains some or all of the five main characteristics of a link:

It uses the HTML element "a" with the attribute "href" (HREF is an abbreviation for "Hypertext REFerence" [12] ) and optionally also the attributes "title", "target", and "class" or "id":

<a href="URL" title="link title" target="link target" class="link class">link label</a>

To embed a link into a web page, blogpost, or comment, it may take this form:

<a href="https://example.com/">Example</a>

In a typical web browser, this would display as the underlined word "Example" in blue, which when clicked would take the user to the example.com website. This contributes to a clean, easy to read text or document.

By default, browsers will usually display hyperlinks as such:

When the cursor hovers over a link, depending on the browser and graphical user interface, some informative text about the link can be shown, popping up, not in a regular window, but in a special hover box, which disappears when the cursor is moved away (sometimes it disappears anyway after a few seconds, and reappears when the cursor is moved away and back). Mozilla Firefox, IE, Opera, and many other web browsers all show the URL. In addition, the URL is commonly shown in the status bar.

Normally, a link opens in the current frame or window, but sites that use frames and multiple windows for navigation can add a special "target" attribute to specify where the link loads. If no window exists with that name, a new window is created with the ID, which can be used to refer to the window later in the browsing session.

Creation of new windows is probably the most common use of the "target" attribute. To prevent accidental reuse of a window, the special window names "_blank" and "_new" are usually available, and always cause a new window to be created. It is especially common to see this type of link when one large website links to an external page. The intention in that case is to ensure that the person browsing is aware that there is no endorsement of the site being linked to by the site that was linked from. However, the attribute is sometimes overused and can sometimes cause many windows to be created even while browsing a single site.

Another special page name is "_top", which causes any frames in the current window to be cleared away so that browsing can continue in the full window.

History

Douglas Engelbart and his team at SRI, 1969 SRI ARC Engelbart Nov 1969.jpg
Douglas Engelbart and his team at SRI, 1969

The term "link" was coined in 1965 (or possibly 1964) by Ted Nelson at the start of Project Xanadu. Nelson had been inspired by "As We May Think", a popular 1945 essay by Vannevar Bush. In the essay, Bush described a microfilm-based machine (the Memex) in which one could link any two pages of information into a "trail" of related information, and then scroll back and forth among pages in a trail as if they were on a single microfilm reel.

In a series of books and articles published from 1964 through 1980, Nelson transposed Bush's concept of automated cross-referencing into the computer context, made it applicable to specific text strings rather than whole pages, generalized it from a local desk-sized machine to a theoretical proprietary worldwide computer network, and advocated the creation of such a network. Though Nelson's Xanadu Corporation was eventually funded by Autodesk in the 1980s, it never created this proprietary public-access network. Meanwhile, working independently, a team led by Douglas Engelbart (with Jeff Rulifson as chief programmer) was the first to implement the hyperlink concept for scrolling within a single document (1966), and soon after for connecting between paragraphs within separate documents (1968), with NLS. Ben Shneiderman working with graduate student Dan Ostroff designed and implemented the highlighted link in the HyperTIES system in 1983. HyperTIES was used to produce the world's first electronic journal, the July 1988 Communications of ACM, which was cited as the source for the link concept in Tim Berners-Lee's Spring 1989 manifesto for the Web. In 1988, Ben Shneiderman and Greg Kearsley used HyperTIES to publish "Hypertext Hands-On!", the world's first electronic book.[ citation needed ]

A database program HyperCard was released in 1987 for the Apple Macintosh that allowed hyperlinking between various pages within a document, as well as to other documents — even separate applications — on the same computer; [13] it was probably the first use of the word "hyperlink". [14] In 1990, Windows Help, which was introduced with Microsoft Windows 3.0, had widespread use of hyperlinks to link different pages in a single help file together; in addition, it had a visually different kind of hyperlink that caused a popup help message to appear when clicked, usually to give definitions of terms introduced on the help page. The first widely used open protocol that included hyperlinks from any Internet site to any other Internet site was the Gopher protocol from 1991. It was soon eclipsed by HTML after the 1993 release of the Mosaic browser (which could handle Gopher links as well as HTML links). HTML's advantage was the ability to mix graphics, text, and hyperlinks, unlike Gopher, which just had menu-structured text and hyperlinks.

While hyperlinking among webpages is an intrinsic feature of the web, some websites object to being linked by other websites; some have claimed that linking to them is not allowed without permission.

Contentious in particular are deep links, which do not point to a site's home page or other entry point designated by the site owner, but to content elsewhere, allowing the user to bypass the site's own designated flow, and inline links, which incorporate the content in question into the pages of the linking site, making it seem part of the linking site's own content unless an explicit attribution is added. [15]

In certain jurisdictions it is or has been held that hyperlinks are not merely references or citations, but are devices for copying web pages. In the Netherlands, Karin Spaink was initially convicted in this way of copyright infringement by linking, although this ruling was overturned in 2003. The courts that advocate this view see the mere publication of a hyperlink that connects to illegal material to be an illegal act in itself, regardless of whether referencing illegal material is illegal. In 2004, Josephine Ho was acquitted of 'hyperlinks that corrupt traditional values' in Taiwan. [16]

In 2000, British Telecom sued Prodigy, claiming that Prodigy infringed its patent ( U.S. Patent 4,873,662 ) on web hyperlinks. After litigation, a court found for Prodigy, ruling that British Telecom's patent did not cover web hyperlinks. [17]

In United States jurisprudence , there is a distinction between the mere act of linking to someone else's website, and linking to content that is illegal (e.g., gambling illegal in the US) or infringing (e.g., illegal MP3 copies). [18] Several courts have found that merely linking to someone else's website, even if by bypassing commercial advertising, is not copyright or trademark infringement, regardless of how much someone else might object. [19] [20] [21] Linking to illegal or infringing content can be sufficiently problematic to give rise to legal liability. [22] [23] [24] Compare [25] for a summary of the current status of US copyright law as to hyperlinking, see the discussion regarding the Arriba Soft and Perfect 10 cases.

Somewhat controversially, Vuestar Technologies has tried to enforce patents applied for by its owner, Ronald Neville Langford, [26] around the world relating to search techniques using hyperlinked images to other websites or web pages. [27]

See also

Related Research Articles

HTML Hypertext Markup Language

The HyperText Markup Language, or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript.

Hypertext Text with references (links) to other text that the reader can immediately access

Hypertext is text displayed on a computer display or other electronic devices with references (hyperlinks) to other text that the reader can immediately access. Hypertext documents are interconnected by hyperlinks, which are typically activated by a mouse click, keypress set, or screen touch. Apart from text, the term "hypertext" is also sometimes used to describe tables, images, and other presentational content formats with integrated hyperlinks. Hypertext is one of the key underlying concepts of the World Wide Web, where Web pages are often written in the Hypertext Markup Language (HTML). As implemented on the Web, hypertext enables the easy-to-use publication of information over the Internet.

World Wide Web System of interlinked hypertext documents accessed over the Internet

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, which may be interlinked by hyperlinks, and are accessible over the Internet. 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. The World Wide Web is not synonymous with the Internet, which pre-dated the Web in some form by over two decades and upon which technologies the Web is built.

Wireless Markup Language Markup language intended for devices that implement the Wireless Application Protocol specification

Wireless Markup Language (WML), based on XML, is a now-obsolete markup language intended for devices that implement the Wireless Application Protocol (WAP) specification, such as mobile phones. It provides navigational support, data input, hyperlinks, text and image presentation, and forms, much like HTML. It preceded the use of other markup languages now used with WAP, such as HTML itself, and XHTML.

Bookmarklet

A bookmarklet is a bookmark stored in a web browser that contains JavaScript commands that add new features to the browser. Bookmarklets are JavaScripts stored as the URL of a bookmark in a web browser or as a hyperlink on a web page. Bookmarklets are usually small snipets of JavaScript executed when user clicks on them. Regardless of whether bookmarklet utilities are stored as bookmarks or hyperlinks, they add one-click functions to a browser or web page. When clicked, a bookmarklet performs one of a wide variety of operations, such as running a search query or extracting data from a table. For example, clicking on a bookmarklet after selecting text on a webpage could run an Internet search on the selected text and display a search engine results page.

In HTML and XHTML, an image map is a list of coordinates relating to a specific image, created in order to hyperlink areas of the image to different destinations. For example, a map of the world may have each country hyperlinked to further information about that country. The intention of an image map is to provide an easy way of linking various parts of an image without dividing the image into separate image files.

An HTML element is a type of HTML document component, one of several types of HTML nodes. HTML document is composed of a tree of simple HTML nodes, such as text nodes, and HTML elements, which add semantics and formatting to parts of document. Each element can have HTML attributes specified. Elements can also have content, including other elements and text.

URL redirection, also called URL forwarding, is a World Wide Web technique for making a web page available under more than one URL address. When a web browser attempts to open a URL that has been redirected, a page with a different URL is opened. Similarly, domain redirection or domain forwarding is when all pages in a URL domain are redirected to a different domain, as when wikipedia.com and wikipedia.net are automatically redirected to wikipedia.org.

XML Linking Language, or XLink, is an XML markup language and W3C specification that provides methods for creating internal and external links within XML documents, and associating metadata with those links.

A query string is a part of a uniform resource locator (URL) that assigns values to specified parameters. A query string commonly includes fields added to a base URL by a Web browser or other client application, for example as part of an HTML form.

A lightweight markup language (LML), also termed a simple or humane markup language, is a markup language with simple, unobtrusive syntax. It is designed to be easy to write using any generic text editor and easy to read in its raw form. Lightweight markup languages are used in applications where it may be necessary to read the raw document as well as the final rendered output.

The anchor text, link label or link text is the visible, clickable text in an HTML hyperlink. The term "anchor" was used in older versions of the HTML specification for what is currently referred to as the a element, or <a>. The HTML specification does not have a specific term for anchor text, but refers to it as "text that the a element wraps around". In XML terms, the anchor text is the content of the element, provided that the content is text.

In the context of a web browser, a frame is a part of a web page or browser window which displays content independent of its container, with the ability to load content independently. The HTML or media elements shown in a frame may come from a different web site as the other elements of content on display, although this practice, known as framing, is today often regarded as a violation of same-origin policy and has been considered a form of copyright infringement.

Microformats (μF) are a set of defined HTML classes created to serve as consistent and descriptive metadata about an element, designating it as representing a certain type of data. They allow software to process the information reliably by having set classes refer to a specific type of data rather than being arbitrary. Microformats emerged around 2005 and were predominantly designed for use by search engines and aggregators such as RSS.

Microdata is a WHATWG HTML specification used to nest metadata within existing content on web pages. Search engines, web crawlers, and browsers can extract and process Microdata from a web page and use it to provide a richer browsing experience for users. Search engines benefit greatly from direct access to this structured data because it allows them to understand the information on web pages and provide more relevant results to users. Microdata uses a supporting vocabulary to describe an item and name-value pairs to assign values to its properties. Microdata is an attempt to provide a simpler way of annotating HTML elements with machine-readable tags than the similar approaches of using RDFa and microformats.

HTML attributes are special words used inside the opening tag to control the element's behaviour. HTML attributes are a modifier of an HTML element type. An attribute either modifies the default functionality of an element type or provides functionality to certain element types unable to function correctly without them. In HTML syntax, an attribute is added to an HTML start tag.

XHTML+RDFa is an extended version of the XHTML markup language for supporting RDF through a collection of attributes and processing rules in the form of well-formed XML documents. XHTML+RDFa is one of the techniques used to develop Semantic Web content by embedding rich semantic markup. Version 1.1 of the language is a superset of XHTML 1.1, integrating the attributes according to RDFa Core 1.1. In other words, it is an RDFa support through XHTML Modularization.

History of hypertext

Hypertext is text displayed on a computer or other electronic device with references (hyperlinks) to other text that the reader can immediately access, usually by a mouse click or keypress sequence. Early conceptions of hypertext defined it as text that could be connected by a linking system to a range of other documents that were stored outside that text. In 1934 Belgian bibliographer, Paul Otlet, developed a blueprint for links that telescoped out from hypertext electrically to allow readers to access documents, books, photographs, and so on, stored anywhere in the world.

A canonical link element is an HTML element that helps webmasters prevent duplicate content issues in search engine optimization by specifying the "canonical" or "preferred" version of a web page. It is described in RFC 6596, which went live in April 2012.

Front-end web development is the development of the graphical user interface of a website, through the use of HTML, CSS, and JavaScript, so that users can view and interact with that website.

References

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  2. "Tabbed browsing". computerhope.com. Retrieved July 26, 2021.
  3. Brusilovski, Peter; Kommers, Piet; Streitz, Norbert (1996-05-15). Multimedia, Hypermedia, and Virtual Reality: Models, Systems, and Application: First International Conference, MHVR'94, Moscow, Russia September (14–16), 1996. Selected Papers. Springer Science & Business Media. ISBN   9783540612827. Archived from the original on 2018-02-07.
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  5. "HTML, Web Browsers, and Other Paraphernalia". Archived from the original on July 4, 2013.
  6. Wikipedia: the missing manual By John Broughton, 2008, ISBN   0-596-51516-2, p. 75 Archived 2018-02-07 at the Wayback Machine
  7. "Hypergrid – OpenSim". Opensimulator.org. 2012-03-04. Retrieved 2012-10-25.
  8. "Creating, Saving, and Loading Spaces – Cobalt – DukeWiki". Wiki.duke.edu. 2009-04-21. Archived from the original on 2012-12-21. Retrieved 2012-10-25.
  9. "Definition of Permanent Link (Permalink)". techopedia.com. Retrieved Oct 31, 2018.
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  11. "The Average Lifespan of a Webpage". November 8, 2011. Archived from the original on September 8, 2016. Retrieved Oct 31, 2018.
  12. Tim Berners-Lee. "Making a Server ("HREF" is for "hypertext reference")". W3.org. Archived from the original on 2012-10-25. Retrieved 2012-10-25.
  13. (Atkinson, Bill?) (1987). "3". Hypercard User's Guide (PDF) (1 ed.). Apple Computer Inc. p. 49.
  14. Lasar, Matthew (May 25, 2019). "30-plus years of HyperCard, the missing link to the Web". ArsTechnica. Retrieved July 26, 2021.
  15. See Arriba Soft case. The Ninth Circuit decision in this case is the first important decision of a US court on linking. In it the Ninth Circuit held the deep linking by Arriba Soft to images on Kelly's website to be legal under the fair use doctrine.
  16. "The prosecution of Taiwan sexuality researcher and activist Josephine Ho" (PDF). Sex.ncu.edu.tw. Archived from the original (PDF) on February 8, 2012. Retrieved 2012-10-25.
  17. CNET News.com, Hyperlink patent case fails to click. August 23, 2002.
  18. Cybertelecom:: Legal to Link?   The Internet Archive. Retrieved June 11, 2012.
  19. Ford Motor Company v. 2600 Enterprises, 177 F.Supp.2d 661 (EDMi December 20, 2001)
  20. American Civil Liberties Union v. Miller, 977 F.Supp. 1228 (ND Ga. 1997)
  21. Ticketmaster Corp. v. Tickets.Com, Inc., No. 99-07654 (CD Calif. March 27, 2000)
  22. Intellectual Reserve v. Utah Lighthouse Ministry, Inc. Archived 2008-12-20 at the Wayback Machine , 75 FSupp2d 1290 (D Utah 1999)
  23. Universal City Studios Inc v Reimerdes, 111 FSupp2d 294 (DCNY 2000)
  24. Comcast of Illinois X LLC v. Hightech Elec. Inc. Archived 2008-12-17 at the Wayback Machine , District Court for the Northern District of Illinois, Decision of July 28, 2004, 03 C 3231
  25. Perfect 10 v. Google Archived 2008-12-17 at the Wayback Machine , Decision of February 21, 2006, Case No. CV 04-9484 AHM (CD Cal. 2/21/06), CRI 2006, 76–88 No liability for thumbnail links to infringing content
  26. TelecomTV – TelecomTV One – News Archived 2008-12-23 at the Wayback Machine
  27. All your Interwibble is belong to us, Silvie Barak, The Inquirer, 21 February 2009

Further reading