This paper presents a formal framework called LKO for the dependable devel-opment of knowledge—based systems(KBSs)．LKO combines logic programming and ob-ject—oriented programming，where logieal objects are viewed as abstractions with states，constraints，behaviors and inheritance．Logical object supports several knowledge repre-sentations such as frame，rule，semantic network and blackboard．So it may be used as a formalism of knowledge and requirements of KBSs．After iterations of specification modi-fication and verification in terms of knowledge acquisition，prototypes might be correctly formed．