Link relation

Alink relationis a descriptive attribute attached to ahyperlinkin 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.

InHTMLthese are designated with therelattribute onlink,a,orareaelements. Example uses include the standard way of referencingCSS,<link rel= "stylesheet" href= "example.css" />,which indicates that the external resource linked to with thehrefattribute is a stylesheet, so aweb browserwill generally fetch this file to render the page. Another example isrel= "shortcut icon"for the popularfaviconicon.

Link relations are used in somemicroformats(e.g.rel= "tag"fortagging), inXHTML Friends Network(XFN), and in theAtom standard,inXLink,as well as in HTML. Standardized link relations are one of the foundations ofHATEOASas they allow the user agent to understand the meaning of the available state transitions in aRepresentational State Transfersystem.

TheInternet Engineering Task Force(IETF) has a registry of standardized link relations,and a procedure for extending it defined in RFC 5988.HTML5also defines valid link relations.

In HTML4, therev attributeof a link is also defined, which defines the relationship between the resources. The attribute is removed inHTML5.

Semantic Web implementation

TheRDFtyped links are fundamental inLOD datasetsfor identifying the relationship (predicate) type ofRDF triples,contributing to the automatic processability of machine-readable statements of theGiant Global Graphon theSemantic Web.The typed links in RDF are expressed as the value of therdf:typeproperty, defining the relationship type using well-establishedcontrolled vocabularyterms or definitions from LOD datasets such as

<rdf:typerdf:resource="http://schema.org/Person"/>

External links

• rel values defined in HTML 4
• rel values to be defined in HTML5
• rel values which are defined in some specification
• WHATWG blog entry on link relations