A catalog holds information about a set of objects, typically classified using terms taken from a given thesaurus Mediated access to a collection of catalogs over the same domain therefore requires some strategy to deal with multiple thesauri, which represent different classifications for the same domain This paper proposes an approach using online mapping rate estimations to define weighted relationships between terms of distinct thesauri The mediator then uses such relationships to remap keyword-based queries to the different catalogs Moreover, query answers provide valuable feedback to adjust the relationship weights, thereby improving the mediator accuracy.