1. An apparatus for information retrieval, comprising: a computer system being programmed to receive a query from a remotely located user system via a network, the query specifying one or more numerical data constraints and contextual constraints; said computer system including a memory storing a computer-searchable electronic index, the index comprising a plurality of entries, each of the index entries representing an item of numerical data extracted from at least one of a plurality of electronic source documents including one or more natural language documents; said computer system being further programmed to determine the relevancy of the query to each of one or more of the index entries based at least partly on a comparison between the numerical data constraint and the index entry's item of numerical data, and at least partly on a comparison between the contextual constraint and contextual information extracted from the corresponding source document from which the index entry's item of numerical data was extracted.