Résumé
In the rules considered, the conclusion may contain existentially quantified variables, which makes reasoning tasks (as deduction) non-decidable. These rules have the same logical form as TGD (tuple generating dependencies) in databases and as conceptual graph rules. We extend known decidable cases by combining backward and forward chaining schemes, in association with a graph that captures exactly the notion of dependency between rules. Finally, we draw a map of known decidable cases, including an extension obtained by combining our approach with very recent results on TGD.