This paper describes performance of an interpreter uncovering meanings of prepositions in "master" - preposition - "slave" constructions. The basis of the semantic interpreter is a set of "if A, than B" rules, with the left parts containing lexical and semantic markers of the "masters" and the "slaves" and morphological markers of the "slaves" (cases) and the right parts containing the meanings of the prepositions which should be attributed if the conditions of the left parts are fulfilled. It is described how, on the basis of the interpreter, the basic onto-sematic rules can be formalized to be implemented into an onto-sematic analyzer and how performance of the analyzer can be improved with implementation of new rules.