1. A method of allowing access to data over a distributed data processing system, the method comprising: providing an automated infrastructure for the exchange of information between multiple self-interested parties; providing a trusted server with at least one data warehouse for the storage of said information, wherein the trusted server includes a processor; associating a price rule with particular data records of said information which establishes a cost of accessing said particular data records, and which controls the access to that data; wherein said price rule enables a data owner associated with said data to specify a different price for different types and amounts of information access; within said trusted server, providing a data processing platform which is accessible to multiple third-party data processing software programs which operate as software agents; wherein a plurality of seller-side software agents have defined relationships to said price rules and associated data records, and maintain absolute access control to said data records; wherein a plurality of buyer-side software agents have regulated query access to said data processing platform and may request pricing information from said seller-side software agents; wherein said plurality of seller-side software agents and said plurality of buyer-side software agents operate as persistent data processing systems which interact with one another repeatedly over time and which thus define a virtual marketplace.