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Alink relation is a descriptive attribute attached to ahyperlink 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.
InHTML these are designated with therel attribute onlink,a, orarea elements. Example uses include the standard way of referencingCSS,<link rel="stylesheet" href="example.css" />, which indicates that the external resource linked to with thehref attribute is a stylesheet, so aweb browser will generally fetch this file to render the page. Another example isrel="shortcut icon" for the popularfavicon icon.[1][2]
Link relations are used in somemicroformats (e.g.rel="tag" fortagging), inXHTML Friends Network (XFN), and in the Atom standard, inXLink, as well as in HTML. Standardized link relations are one of the foundations ofHATEOAS as they allow the user agent to understand the meaning of the available state transitions in aRepresentational State Transfer system.
TheInternet Engineering Task Force (IETF) has a registry of standardized link relations,[3] and a procedure for extending it defined in RFC 5988.HTML5 also defines valid link relations.[4]
In HTML4, therev attribute of a link is also defined, which defines the relationship between the resources. The attribute is removed inHTML5.
TheRDF typed links are fundamental inLOD datasets for identifying the relationship (predicate) type ofRDF triples, contributing to the automatic processability of machine-readable statements of theGiant Global Graph on theSemantic Web. The typed links in RDF are expressed as the value of therdf:type property, defining the relationship type using well-establishedcontrolled vocabulary terms or definitions from LOD datasets such as
<rdf:typerdf:resource="http://schema.org/Person"/>
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