14. The combination of computer program products of claim 13, further comprising: a user interface module that receives the user query and provides it to the query router, and that receives the extracted data fields from the aggregation engine and displays them to the user.
13. A combination of computer program products, executable by one or more computers attached to a network, for assisting a user to query for information available from information sources attached to the network, the computer program product comprising: a query router that receives the user query and selects the one or more information sources most relevant to the user query; a wrapper description database containing a description of each of the information sources, each description written in a wrapper description language comprising facilities for specifying an entire regular expression in terms of component regular expressions such that, upon recognition of one component regular expression of the entire regular expression, actions can be executed with variables bound as of the time of recognition of the component regular expression, the actions actually being executed only if the entire regular expression is also recognized; an aggregation engine that receives from the query router the relevant information sources, and formats the user query for each relevant information source according to the description of each relevant information source in the wrapper description database, and that extracts data fields relevant to the user query from responses returned from each of the relevant information sources according to the description of the relevant information source returning each response; and an input/output manager that transmits the formatted query to each of the relevant information sources via the network, and provides the responses returned to the user query from the relevant information sources to the aggregation engine.