C-POREL is a distributed relational data base management system, with full distribution transparency. A relation can be horizontally fragmented into several subrelations allocated to different 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 reduce relations involved. Distribution dependent attributes of a relational schema are defined in this paper. An optimization approach of distributed join w...

Key words: type theory，inductive type，w-set;