Abstract: The situation that some objects immigrate the system and some objects emigrate the system simultaneously exists in dynamical information systems.In this paper, a calculation method for core attributes is proposed in information view.First, the changing mechanism of condition entropy is analyzed from three different cases, whick include the objects' immigration or emigration and that this two cases coexisted.Based on the mechanism, the new condition entropy is computed quickly by support matrixes and incremental matrixes.These matrixes can constructed by computing the objects immigrated or emmigrated at the same time.Then core attributes are obtained quickly.Finally, the validity of the method has been depicted by a practical example.

Key words: dynamic information systems, incremental matrix, support matrix, conditional entropy, core attributes