自然な構造の階層的知識

抄録

It is important to formalize operations like circumscription on hierarchical knowledge in which notions of frame and inheritance are used. We formulate meanings of hierarchical knowledge by transforming it into predicate logic formulas. In this formulation we define two useful classes of formulas called (1) meaningful non-recursive definite clause and (2) non-recursive hierarchical definite clause (HDC). The most important feature of (2) is that if we circumscribe axiom of HDC, the result is also HDC. This feature gives us a criterion of applying circumscription to hierarchical knowledge. We also find a condition in circumscription that guides meaningful non-recursive definite clause to the same class of clauses.