Query processing in multidatabase systems

A novel algorithm to efficiently process a query in a multidatabase environment is devised. The proposed approach reduces data movement between sites and local processing time by allowing local selection and projection for a user query. Also, the algorithm efficiently removes null values incurred due to an outer join by generating the results as a set of sets, gives users more accurate information by presenting all data values for an overlap part, and gives users flexibility by enabling them to define their own processing strategy at a query time