Namespaces where added to XML to increase its modularisation and the reuse of XML vocabularies in conjunction with XML Schemas. They are also used in the Semantic Web for the same purpose.
The fifth layer is the ontologyitself. Ontologies are the key components to the Semantic Web because theycontain the domain “knowledge” that defines concepts and their relationships toeach other. Although RDF does have some capabilities to represent relationshipbetween resources, it lacks the semantic richness and inference capacity thatthe OWL provides. OWL is built on RDF, adding greater vocabulary forspecifying relationships between classes, individuals, propertycharacteristics, and enumerated classes, that allows for developing richontologies.
Any suggestions about PhD thesis on Semantic Web? - ANSWERS
The Semantic Web encourages the free flow of information but also it should guarantee group boundaries, i.e. restrictions to information access and thus privacy.