Characterization of unknown values with implicit predicate

In general, null values are interpreted as unknown value or inapplicable value. This paper proposes a new approach for solving the unknown value problems with Implicit Predicate (IP). The IP serves as a descriptor corresponding to a set of the unknown values, thereby expressing the semantics of them. In this paper, we demonstrate that the IP is capable of (l) enhancing the semantic expressiveness of the unknown values, (2) entering incomplete information into database and (3) exploiting the information and a variety of inference rules in database to reduce the uncertainties of the unknown values.