Searching online catalog databases by shoppers is improved by performing similarity searching on searches performed by the shopper, in conjunction with adjusting the similarity metric used during the search to interactively improve the relevance of the resulting search results to the shopper. This involves using relevance feedback and/or product redefinition to learn the “implied concept” of the shopper's stated product requirements; that is, the quality of the search results is enhanced through understanding the concept implied by the shopper's queries by, for example, learning from the product results marked as “relevant” or “irrelevant” by the shopper. This approach is in contrast with attempts to enhance search results using, for example, the shopper's past orders or previous actions, or the past orders or previous actions of other shoppers who may have a purchase history similar to that of the current shopper.