In the paper we present Rough Set approach to reasoning in incomplete
information systems. We propose reduction of knowledge that eliminates
only that information, which is not essential from the point of view
of classification or decision making. In our approach we make only one
assumption about unknown values: the real value of a missing attribut
e is one from the attribute domain. However, we do not assume which on
e. We show how to find decision rules directly from such an incomplete
decision table, which are as little non-deterministic as possible and
have minimal number of conditions. (C) 1998 Published by Elsevier Sci
ence Inc. All rights reserved.