1. A method for retrieving information from databases, said databases being structured or unstructured, said databases being homogeneous or heterogeneous, wherein retrieval is performed through visual queries on dynamic taxonomies, said dynamic taxonomies being an organization of concepts that ranges from a most general concept to a most specific concept, said concepts and their organization being called an intension, items in said databases being classified under one or more concepts, said items and their classification being called an extension, said method comprising, given an initial current subset of interest: using a computer for providing a reduced taxonomy for the current subset of interest; using the computer for refining the current subset of interest of said reduced taxonomy with the combination of one or more taxonomy concepts through Boolean operations; and using the computer for iteratively repeating said steps of providing a reduced taxonomy for the current subset of interest to further refine said retrieval and of refining the current subset of interest, wherein: said initial subset of interest includes all the items in the extension of the dynamic taxonomy or a subset of them; said reduced taxonomy is derived from said taxonomy by using the computer for pruning concepts under which no item in said current subset of interest is classified; said step of pruning concepts includes eliminating from the taxonomy all the concepts under which no item in the current subset of interest is classified, or preventing said concepts from being displayed, or preventing said concepts from being selected in order to refine interest sets; said step of providing a reduced taxonomy either reports only the concepts belonging to the reduced taxonomy or, for each such concept also reports how many items in the current interest set are classified under the concept; in said extension, there exists at least one item such that said item is classified under at least two different concepts such that each of said two concepts is neither an ancestor nor a descendant of the other concept in the intension.