Rel attribute
Encyclopedia
A link relation is a descriptive attribute attached to a hyperlink
in order to define the type of the link, or the relationship between the source and destination resources. The attribute can be used by automated systems, or can be presented to a user in a different way.
In HTML
these are designated with the rel attribute on link, a or area tags. Example uses include the standard way of referencing CSS
, which indicates that the external resource linked to with the href attribute is a stylesheet, so a web browser
will generally fetch this file to render the page. Another example is rel=favicon for the popular favicon
icon.
Link relations are used in some microformat
s (e.g. rel="tag" for tagging
), in XHTML Friends Network
(XFN), and in the Atom standard
, in XLink
, as well as in HTML. Standardized link relations are one of the foundations of HATEOAS
as they allow the user agent to understand the meaning of the available state transitions in a REST
system.
The Internet Engineering Task Force
(IETF) has a registry of standardized link relations, and a procedure for extending it defined in RFC 5988. HTML 5
also defines valid link relations.
.
Hyperlink
In computing, a hyperlink is a reference to data that the reader can directly follow, or that is followed automatically. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text with hyperlinks...
in order to define the type of the link, or the relationship between the source and destination resources. The attribute can be used by automated systems, or can be presented to a user in a different way.
In HTML
HTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
these are designated with the rel attribute on link, a or area tags. Example uses include the standard way of referencing CSS
Cascading Style Sheets
Cascading Style Sheets is a style sheet language used to describe the presentation semantics of a document written in a markup language...
, which indicates that the external resource linked to with the href attribute is a stylesheet, so a web browser
Web browser
A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
will generally fetch this file to render the page. Another example is rel=favicon for the popular favicon
Favicon
A favicon , also known as a shortcut icon, Web site icon, URL icon, or bookmark icon, is a file containing one small icons, most commonly 16×16 pixels, associated with a particular Web site or Web page...
icon.
Link relations are used in some microformat
Microformat
A microformat is a web-based approach to semantic markup which seeks to re-use existing HTML/XHTML tags to convey metadata and other attributes in web pages and other contexts that support HTML, such as RSS...
s (e.g. rel="tag" for tagging
Tag (metadata)
In online computer systems terminology, a tag is a non-hierarchical keyword or term assigned to a piece of information . This kind of metadata helps describe an item and allows it to be found again by browsing or searching...
), in XHTML Friends Network
XHTML Friends Network
XHTML Friends Network is an HTML microformat developed by Global Multimedia Protocols Group that provides a simple way to represent human relationships using links. XFN enables web authors to indicate relationships to the people in their blogrolls by adding one or more keywords as the rel...
(XFN), and in the Atom standard
Atom (standard)
The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol is a simple HTTP-based protocol for creating and updating web resources.Web feeds allow software programs to check for updates published on a...
, in XLink
XLink
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.-The XLink specification:...
, as well as in HTML. Standardized link relations are one of the foundations of HATEOAS
HATEOAS
HATEOAS, an abbreviation for Hypermedia as the Engine of Application State, is a constraint of the REST application architecture that distinguishes it from most other network application architectures. The principle is that a client interacts with a network application entirely through hypermedia...
as they allow the user agent to understand the meaning of the available state transitions in a REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
system.
The Internet Engineering Task Force
Internet Engineering Task Force
The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...
(IETF) has a registry of standardized link relations, and a procedure for extending it defined in RFC 5988. HTML 5
HTML 5
HTML5 is a language for structuring and presenting content for the World Wide Web, and is a core technology of the Internet originally proposed by Opera Software. It is the fifth revision of the HTML standard and is still under development...
also defines valid link relations.
rev attribute
In HTML 4, rev attribute of a link is also defined, which defines the reversed relationship between the resources. The attribute is removed in HTML 5HTML 5
HTML5 is a language for structuring and presenting content for the World Wide Web, and is a core technology of the Internet originally proposed by Opera Software. It is the fifth revision of the HTML standard and is still under development...
.