Incremental computation of materialized outer-join views

The algorithm for maintaining materialized outer-join views is proposed to compute the secondary delta by the independent computation of terms. In this algorithm, select project outer-join (SPOJ) views are rewritten as the join-disjunctive normal form first. Then the independent computation of terms is derived from every normal term. Finally common sub-expressions extracted from all of the computation terms are utilized to compute the secondary delta of materialized outer-join views. Experimental results show that the algorithm can reduce the computational cost effectively compared with other counterparts under the same conditions, and furthermore it poses no restrictions on SPOJ views.