4. The method according to claim 1 , further comprising determining a nature of information being provided by a data source in response to a composed sub-query for that data source, and determining a cost associated with obtaining the information.
4. The method according to claim 1 , further comprising determining a nature of information being provided by a data source in response to a composed sub-query for that data source, and determining a cost associated with obtaining the information. 5. The method according to claim 4 , wherein the cost is based on at least one of memory and time needed for the composed sub-query.