Yves Moinard Donner la préférence au défaut le plus spécifique , RFIA'87 (Reconnaissance des Formes et Intelligence Artificielle) , Dunod (Bordas) , Antibes , 1123--1132 , nov , 1987 Abstract One way of knowledge representation fitting with rules with exceptions is default theory [Reiter80]. A short presentation of this theory emphasizes the utility of introducing a notion of preference by specificity. In case of conflict, it is natural to choose the default which has the more specific prerequisite. Touretzky, from his work about the semantic network NETL (which concerns IS-A hierarchies with exceptions), proposed one of the first solutions introducing specificity in default theory [Touretzky 84]. Drawing inspiration from this work with a different point of view, Poole made another proposition but he has reached almost thesame notion [Poole 85]. Both solutions seem at first sight to present severe limitations. We study here the notion of preference by specificity and we delimit its boundaries, with elementary principles. We specify the relations between this notion and shortest path. This web site is maintained by René Quiniou using the Weave system from the Caravel project: http://www-caravel.inria.fr. Last modification: 10-07-2011 09:54:25 Version française