8. The method according to claim 1 , and comprising: collecting information regarding a topology and performance characteristics of the data sources; receiving a query from a user regarding the data; determining a query plan responsively to the query and to the information regarding the topology and performance characteristics; and generating a response to the query in accordance with the query plan.
9. The method according to claim 8 , wherein the data sources are distributed among a set of autonomous organizations comprising at least first and second organizations, wherein the user submitting the query belongs to the first organization, and wherein determining the query plan comprises selecting, responsively to the performance characteristics, at least one of the data sources of the second organization for use in responding to the query.