As the tableau algorithm would produce a lot of description overlaps when judging the satisfiabilities of concepts（thus wasting much space）,a clause-based enhancing mode designed for the language ALCN is proposed.This enhancing mode constructs a disjunctive normal form on concept expressions and keeps only one conjunctive clause,and then substitutes the obtained succinctest conjunctive clause for sub-concepts set in the labeling of nodes of a completion tree constructed by the tableau algorithm （such a process may be repeated as many times as needed）.Due to the avoidance of tremendous descriptions redundancies caused by applying ∩- and ∪-rules of the ordinary tableau algorithm,this mode greatly improves the spatial performance as a result.An example is given to demonstrate the application of this enhancing mode and its reduction in the cost of space. Results show that the improvement is very outstanding.
