The Optimization of Distributed Join in C-POREL System

C-POREL is a distributed relational data base management system, with full distributiontransparency. A relation can be horizontally fragmented into several subrelations allocated todifferent sites. When two or more fragmented relations appear in a join query, many-to-many semijoins between correspondent relations are usually needed in order to fully reducerelations involved. Distribution dependent attributes of a relational schema are defined in thispaper. An optimization approach of distributed join which decreases the amount of trans-mission data by avoiding many-to-many semijoins is given.