Adding similarity to possibilistic logic with fuzzy constants

The authors propose an extension of a Horn-rule sublogic of PLFC (a first-order possibilistic logic programming language dealing with fuzzy constants and fuzzily restricted quantifiers) with similarity-based unification of object constants. At the semantic level, we equip each sort with a fuzzy similarity relation, and at the syntactic level, we replace each precise object constant in the antecedent of a Horn-rule by a variable weight fuzzily "enlarged" by means of a fuzzy similarity relation