RDF Schema
  - RDF schema: kind of dictionary for a domain
- declaration of a set of properties and their corresponding
  semantics
- relationships between vocabulary items from multiple independently
    developed schemas
- Since URI references are used to identify classes and properties in the
    Web, it is possible to create new properties that have a domain or range
    whose value is a class defined in another namespace.
- class system with the objectives:
    
      - sharability for the reusability of metadata definitions
- extensibility: subclass refinement and multiple inheritance
 
- RDF Vocabulary Description Language 1.0 Working Draft 30 April 2002
- To go further... 'ontology' languages: DAML+OIL, W3C WebOnt, inference
    rule languages..
    
  
 

  - everything is a resource: class, property and statement are subclasses
    of resources (nodes with bold outlines)
- properties among resources: range and domain definitions