1. An information retrieval system for generating queries to one or more information sources, said information retrieval system comprising: a demand agent providing: a user interface for allowing a user to specify a search expression; a query specification interface for allowing a user to specify a channel between a first query and a second query wherein the search results for an attribute of said first query are provided as an attribute of said second query; a broker agent providing a search and retrieval element for processing a search expression and creating specific information source search requests; a channel element for associating the results of an attribute of said first query with said second query; a supply agent for receiving said search requests and requesting and obtaining documents from information sources responsive to said search requests.