Conclusion
  - Annotations can be treated as RDF metadata
 
  -  The reuse of current Web standards makes the implementation relatively
    easy
 
  - Open infrastructure 
    
      - RDF schema for defining annotation properties
 
      - XPointer for associating annotations to any XML document
 
      - XLink for presentation
 
      - HTTP for data exchanges
 
    
   
  - Easy to extend (discussion threads)
 
  - Client independent
 
  - Some obstacles remain
    
Scalability issues...
    Robust annotations