“…Hence, the need for mechanisms to assess a degree of similarity among logic descriptions. Previous works on similarity/distance measures and techniques developed for comparing firstorder descriptions are concerned with flexible matching (Esposito, 1992), supervised learning (Bisson, 1992a;Emde, 1996;Domingos, 1995;Sebag, 1997;NienhuysCheng, 1998;Ramon, 2002;Kodratoff, 1986) and unsupervised learning (Thompson, 1989;Ramon, 1999;Bisson, 1992b;Blockeel, 1998). The similarity framework for FOL descriptions presented in the following overcomes some problems that are present in those works: it does not require assumptions and simplifying hypotheses (statistical independence, mutual exclusion) to ease the probability handling, no prior knowledge of the representation language is required and is not based on the presence of 'mandatory' relations, the user must not set weights on the predicates' importance, it can be easily extended to handle negative information, it avoids the propagation of similarity between subcomponents that poses the problem of indeterminacy in associations, it yields a unique value as a result of a comparison, which is more understandable and comfortable for handling, it is based directly on the structure, and not on derived features.…”