(Resource Description Framework) A recommendation from the W3C for creating meta-data structures that define data on the Web. RDF is designed to provide a method for classification of data on Web sites in order to improve searching and navigation (see Semantic Web).

An RDF Schema (RDFS) is a construct that describes the structure of the RDF vocabulary, including the terms used and their interrelationships and properties.

Based on XML
RDF is implemented in XML (RDF/XML) and adds new rules to XML as well as reducing some constraints. For example, it supports flat structures, eliminating the need to have data nested in a hierarchy. RDF is structured as one or more Triples: (1) the subject (what the data are about), (2) the property (an attribute of the subject) and (3) the actual value.

A Common Denominator
RDF serves as a common denominator that allows different sets of vocabulary to be recognized. For example, using the RDF descriptor for zip code would let systems exchange zip code data that use "ZIP" and "ZIPCODE. See SPARQL, OWL, XDI and RSS.