Modern fact databases contain abundant data classified through several classifications.

this paper is based on a different approach. In it the user describes only the structure of the result NF relation in a straightforward and intuitive way. This starting point of our interface affords the possibility of formulating queries in a compact and truly declarative manner - also in those cases which require considerable restructuring among data. In this paper we consider the Prolog-based implementation of the query processing strategy of our interface. Special attention is paid to those principles and techniques in terms of which the representation and manipulation of complex structural relationships of NF relations can be managed in Prolog