Abstract: The incomplete information system with both absent and missing unknown values was studied. The limitation of characteristic class, was pointed out such that not any two elements in a characteristic class were mutually tolerant. The technique of maximal consistent blocks was introduced into characteristic class, and then the concept of characteristic consistent block was proposed. Not only the basic properties about characteristic consistent blocks based rough set were discussed, but also the relationship between characteristic consistent blocks and characteristic relation based rough sets was analyzed. The results showed that by comparing with the characteristic relation, the greater lower approximation and smaller upper approximation could be obtained by characteristic consistent block approach.

Key words: incomplete information system, characteristic relation, characteristic consistent block, rough set