Mediated Systems

Definition from David Martin's paper (Information Broker Project):
"Mediation is a process that permits a user to get information from a wide variety of sources, without having to be aware of the identities, locations, schemas, access mechanisms, or contents of these sources. A component that performs mediation presents a single schema (called mediated schema - our comment) to its requesters, accepts queries expressed in that schema, and handles all the details of getting the appropriate data from relevant information sources (each of which is likely to operate with a different schema)."

• Picture
• Steps in how the queries are answered
  • Receive a query formulated on the unified schema from the user
  • Query reformulation
  • Optimization and execution
  • Translation
  (** For detailed description of the steps above refer to the section on query processing)
• Wrapper as an important component - hides technical and data model heterogeneity.
• Additional problems raised by this specific architecture
• Known implementations
  - TSIMMIS
  - Information Manifold
  - SIMS
  - Carnot
  (** very briefly, may be just mention)