%0 Conference Paper %1 boulicaut00approximation %A Boulicaut, Jean-Francois %A Bykowski, Artur %A Rigotti, Christophe %B PKDD '00: Proceedings of the 4th European Conference on Principles of Data Mining and Knowledge Discovery %C London, UK %D 2000 %I Springer-Verlag %K FCA OntologyHandbook %P 75--85 %T Approximation of Frequency Queries by Means of Free-Sets