Abstract:Attribute reduction is one of the key problems in rough set theory, and determination of core attribute is the basis to solve the problem of attribute reduction. First, by using the tree structure knowledge expression in the decision table, an approach for computing positive and negative regions was introduced. Next, according to changes of positive and negative regions in tree structure decision table relative to the conditional attribute set, an algorithm for computing core attributes was developed. An efficiency of the proposed methods was illustrated by time and space complexities analysis and experimental result in a weather decision table.