QUERY-PROCESSING METHOD FOR MULTIPLE DATABASES WITH A DIFFERENT SET OF ATTRIBUTES

This paper discusses a schema integration and query processing method that enables integrated access to the multiple autonomous databases in the distributed environment with schemata restricted to a set of attr ibutes. This method is based on the construction of a virtual database (VDB) formed over physically distributed component databases. Althoug h user queries are issued to this VDB, these queries are decomposed to the subqueries using the virtual functional dependency (VFD), which i s defined on the VDB and issued to each actual component database. The VDB-based method can obtain more answers that are logically valid tha n those gained from conventional query processing methods. When the VF D formed over a VDB is acyclic among the nodes to which the query refe rs, sound and complete answers can be efficiently calculated.