"RDFa is Semantic Annotation for (X)HTML.
With RDFa, you can easily include extra “structure” in your (X)HTML to indicate a calendar event, contact information, a document license, etc… RDFa is about total publisher control: you choose which attributes to use, which to reuse from other sites, and how to evolve, over time, the meaning of these attributes.
This site tracks RDFa specifications, implementations, and news of all sorts."
OWL is a Web Ontology language. Where earlier languages have been used to develop tools and ontologies for specific user communities (particularly in the sciences and in company-specific e-commerce applications), they were not defined to be compatible with the architecture of the World Wide Web in general, and the Semantic Web in particular.