The implementation of the Semantic Web requires machine-readable information to allow agents to autonomously discover and use information that is normally only human-readable. The current model of the Semantic Web relies upon the coordination of several languages to produce this output. By layering the languages and other pieces as in the diagram, the W3C's Semantic Web effort can build on past successful languages to create new languages tailored to its purpose.
As the figure shows, the foundation of this model consists of previous W3C recommendations XML and XML Namespaces, the W3C specification URI, and the international character encoding system, Unicode. Resource Description Framework and RDF-S use XML syntax to define ways of writing metadata to describe web resources. OWL, the ontology vocabulary, builds on top of RDF to create additional vocabulary for describing classes and relationships.
The following is a listing of the participants in the Semantic Web "layering cake", with a brief description, current status, and links to tutorials and more information. Additionally, OWL-S, a language for describing Semantic Web Services, has been included along with deprecated languages that have since been replaced.
The remainder of the layering diagram (Logic, Proof, Trust, Signature/Encryption) do not currently have W3C recommendations or another united development effort, but some existing work can be found in other sections of this wiki (see Reasoning and Inference Tools and Querying).