Hyperlink
A
hyperlink, or simply a
link, is a
reference in a
hypertext document to another document or other
resource. As such it is similar to a
citation in
literature. Combined with a
data network and suitable access
protocol, a computer can be instructed to fetch the resource referenced.
Hyperlinks are part of the foundation of the
World Wide Web created by
Tim Berners-Lee.
There are a number of ways to format and present hyperlinks on a web page. An
embedded link is one of the more common formats: one or more words of distinctively styled text. The ninth word of this sentence is an
example of an embedded link.
Hyperlinks in HTML
Tim Berners-Lee saw the possibility of using hyperlinks to link any unit of information to any other unit of information over the
Internet. Hyperlinks were therefore integral to the creation of the
World Wide Web.
Links are specified in
HTML using the
(anchor) elements.
XLink: Hyperlinks in XML
The
W3C Recommendation called
XLink describes hyperlinks which 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 also describes
simple links which are unidirectional and therefore offer no more functionality than hyperlinks in HTML.
Hyperlinks in other technologies
Hyperlinks are used in
e-mails,
PDF documents,
word processing documents,
spreadsheets,
Apple's
HyperCard and many others.
A link has two ends, called anchors, and a direction. The link starts at the source anchor and points to the destination anchor. However, the term
link is often used for the source anchor, while the destination anchor is called the link target.
The most common link target 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 a
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 "#
attribute name" appended.
Link behavior in web browsers
A
web browser usually displays a hyperlink in some distinguishing way, e.g. in a different
colour,
font or
style. The behaviour and style of links can be specified using the
Cascading Style Sheets (CSS) language.
In a graphical user interface, the usage of a
mouse cursor may also change into a
hand motif to indicate a link. In most graphical web browsers, links are displayed in underlined blue text when not
cached, but underlined purple text when cached. When the
user activates the link (e.g. by clicking on it with the mouse) the browser will display the target of the link. If the target is not a 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:
*
link destination ("href" pointing to a URL)
*
link label*
link title*
link target*
link class or
link idIt uses the
HTML element "a" with the attribute "href" and optionally also the attributes "title", "target", and "
class" or "id":
"URL" title="link title" target="link target" class="link class">link labelExample: To embed a link into a Page, blogpost, or comment, it may take this form:
BendGovtThus, the complex link string is reduced to, [BendGovt]. This contributes to a clean, easy to read text or document.
When the cursor hovers over a link, depending on the browser and/or graphical user interface, some informative text about the link can be shown:
*It pops 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).
IE and
Mozilla Firefox show the title,
Opera also shows the URL.
*In addition, the URL may be shown in the
status bar.
Normally, a link will open 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 will be loaded. Windows can be named upon creation, and that identifier can be used to refer to it later in the browsing session. If no current window exists with that name, a new window will be created using the ID.
Creation of new windows is probably the most common use of the "target" attribute. In order to prevent accidental reuse of a window, the special window names "_blank" and "_new" are usually available, and will 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.
The
Google search engine uses
PageRank, a measure of
link popularity to determine which page should be ranked first. The more pages that have a hyperlink pointing to a page, the higher rank that page gets. Other factors are important as well; see
PageRank for more information.
The term "hyperlink" 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 essay by
Vannevar Bush. In the essay, Bush described a microfilm-based machine 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. The closest contemporary analogy would be to build a list of bookmarks to topically related Web pages and then allow the user to scroll forward and backward through the list.
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 worldwide computer network, and advocated the creation of such a 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). See
NLS.
While hyperlinking among pages of Internet content has long been considered an intrinsic feature of the Internet, some websites have claimed that linking to them is not allowed without permission.
[For example, see Irisnet (in Dutch).].
In some
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, for example,
Karin Spaink was initially convicted of copyright infringement for linking, although this ruling was overturned in 2003. Although this principle is generally rejected by
digerati [[1]], the courts that adhere to it 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
Japan, it is considered rude to link to a personal website without getting permission beforehand. Because of this, many Japanese artists, and some American artists who have ties to the Japanese CG world
[For example, Fred Gallagher's FredArt.], use the phrase "Link Free" on their websites to indicate that they will not be upset by unauthorized linking.
In 2000,
British Telecom sued
Prodigy claiming that Prodigy infringed its patent () on web hyperlinks. However, after costly
litigation, a
court found for Prodigy, ruling that
British Telecom's patent did not actually cover web hyperlinks.
[CNET News.com, Hyperlink patent case fails to click. August 23, 2002.]Moreover, although there is not much case law to support it, some have argued that hyperlinks could infringe the "making available right" provided in the WIPO Internet treatises.
*
Object hyperlinking*
HTML element*
Linked words.
*
Anatomy and Deployment of Links - an in-depth guide to hyperlinks
*
What is hyperlink - Independent sources / references on web as to what hyperlink in its nature is
*
Links & Law - Overview of legal issues and court rulings involving linking
