1. An information retrieval system having a storage device, a display device and a processor, wherein the processor is configured to: receive from a user a search query including a plurality of keywords; calculate a relevance to a plurality of documents on the basis of the plurality of keywords and an influence set for each keyword; display on the display device documents in the order of relevance; display on the display device the influence set for each keyword; receive changes to the displayed influence set from the user; and recalculate the relevance on the basis of a change to the influence set and displaying on the display device documents in the order of relevance.