Efficient Maintenance of Materialized Outer-Join Views

Queries containing outer joins are common in data warehousing applications. Materialized outer-join views could greatly speed up many such queries but most database systems do not allow outer joins in materialized views. In part, this is because outer-join views could not previously be maintained efficiently when base tables are updated. In this paper we show how to efficiently maintain general outer-join views, that is, views composed of selection, projection, inner and outer joins. Foreign-key constraints are exploited to reduce maintenance overhead. Experimental results show that maintaining an outer-join view need not be more expensive than maintaining an inner-join view.