A link relation is a descriptive attribute attached to a

hyperlink In computing, a hyperlink, or simply a link, is a digital reference providing direct access to Data (computing), data by a user (computing), user's point and click, clicking or touchscreen, tapping. A hyperlink points to a whole document or to ...

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 Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...

these are designated with the attribute on , , or elements. Example uses include the standard way of referencing CSS, , which indicates that the external resource linked to with the attribute is a stylesheet, so a

web browser A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...

will generally fetch this file to render the page. Another example is for the popular favicon icon. Link relations are used in some

microformat Microformats (μF) are predefined HTML markup (like HTML classes) created to serve as descriptive and consistent metadata about elements, designating them as representing a certain type of data (such as contact information, geographic coor ...

s (e.g. 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 Hypermedia as the engine of application state (HATEOAS) is a constraint of the REST software architectural style that distinguishes it from other network architectural styles. With HATEOAS, a client interacts with a network application whose appl ...

as they allow the user agent to understand the meaning of the available state transitions in a

Representational State Transfer REST (Representational State Transfer) is a software architectural style that was created to describe the design and guide the development of the architecture for the World Wide Web. REST defines a set of constraints for how the architecture of ...

system. The

Internet Engineering Task Force The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...

(IETF) has a registry of standardized link relations,IANA link relations registry
/ref> and a procedure for extending it defined in RFC 5988.

HTML5 HTML5 (Hypertext Markup Language 5) is a markup language used for structuring and presenting hypertext documents on the World Wide Web. It was the fifth and final major HTML version that is now a retired World Wide Web Consortium (W3C) recommend ...

also defines valid link relations.HTML Living Standard; 4.12.4 Link types
Web Hypertext Application Technology Working Group In HTML4, the rev attribute of a link is also defined, which defines the relationship between the resources. The attribute is removed in

Semantic Web implementation

The RDF typed links are fundamental in LOD datasets for identifying the relationship (predicate) type of

RDF triple A semantic triple, or RDF triple or simply triple, is the atomic data entity in the Resource Description Framework (RDF) data model. As its name indicates, a triple is a tuple, sequence of three entities that codifies a statement (programming), sta ...

s, contributing to the automatic processability of machine-readable statements of the Giant Global Graph on the

Semantic Web The Semantic Web, sometimes known as Web 3.0, is an extension of the World Wide Web through standards set by the World Wide Web Consortium (W3C). The goal of the Semantic Web is to make Internet data machine-readable. To enable the encoding o ...

. The typed links in RDF are expressed as the value of the rdf:type property, defining the relationship type using well-established

controlled vocabulary A controlled vocabulary provides a way to organize knowledge for subsequent retrieval. Controlled vocabularies are used in subject indexing schemes, subject headings, thesauri, taxonomies and other knowledge organization systems. Controlled v ...

terms or definitions from LOD datasets such as

References

External links

rel values defined in HTML 4rel values to be defined in HTML5rel values which are defined in some specificationWHATWG blog entry on link relations
HTML {{web-stub