Multidatabase query optimization: issues and solutions

Despite the interest in multidatabase systems, research in multidatabase query optimization (MQO) has been scarce. Many researchers perceive the difficulty to be the lack of reliable cost estimates for autonomous component databases. Consequently, some have suggested that this problem degenerates to a distributed query optimization (DQO) problem once cost model coefficients for component databases are found. The authors argue that autonomy and heterogeneity of component databases give rise to a number of issues which make MQO a distinct problem from DQO. Consequently, existing solutions for DQO need to be re-evaluated in the light of these issues. The design of a multidatabase query optimizer, which accounts for the issues highlighted, is discussed. This provides a framework within which further research in MQO can be carried out