Lossless Decomposition if R1∩R2 forms a superkey for either R1 or R2, the decomposition of R is a lossless decomposition 关系模式 R(U) 的分解 r={R1，R2}，则 r 是一个无损连接分解的充要条件是 R1∩R2→R1-R2（或 R1∩R2→R2-R1）成立 BCNF Decomposition Break large into multiple superkey.