The RDF data model is similar to classic conceptual modeling approaches such as Entity-Relationship or Class diagrams, as it is based upon the idea of making statements about resources (in particular Web resources) in the form of Subject-predicate-object expressions. These expression are known as TRIPLES in RDF terminology. The subject denotes the resources, and the predicate denots trait or aspects of the resource and expresses a relationship between the subject and the object. For example, one way to represent the notion "The sky has color blue" in RDF is as the triple: a subject denoting "the sky", a predicate denoting "has the color", and an "object" denoting "blue". RDF is an abstract model with several serialization formats (i.e. file formats), and so the particular way in which a resource or triple is encoded varies from format to format.
This mechanism for describing resources is a major component in what is proposed by the W3C's Semantic Web activities: an evolutionary stage of the WWW in which automated software can store, exchange, and use machine-readable information distributed throughout web, in turn enabling users to deal with the information with greater efficiency and certainty. RDF's simple data modes and ablility to model desparate, abstracy concepts has also led to its increasing use in knowledge management applications unrelated to semantic web activity.
A collection of RDF statements intrinsically represents a labeled, directed multi-graph. As such, an RDF-based data model is more naturally suited to certain kinds of knowledge representaiton than the relational model and other ontological models traditionally used in computing today. However, in practice, RDF data is often persisted in relational database or native representations also called Triplestores, or Quad store if context (i.e. the named graph) is also persited for each RDF triple. As RDFS and OWL demonstrate, additional ontoloty languages can be built upon RDF.