【摘要】 无损联接问题是关系数据库模式设计中十分重要的问题。本文指出,为了确保数据库查询的可靠性,组成数据库模式的关系模式集合,仅仅在整体上无损联接是不够的,还必须满足完全无损联接性。文中表明,A.V.Aho等在文献[1]中提出的关于在MVD环境下完全无损联接的充要条件的定理,仅仅在不存在潜多值相关性的情况下是成立的,并且给出了在潜多值相关性存在的环境下这一问题的某些新的结果。更多还原

【Abstract】 To guarantee complete data relatability and query reliability, it is neccessary that the set of relational schemes which constitute a database schema has completely lossless joins. In this paper we show that the conclusions in reference [1] concerning completely lossless join in the case of MVDs hold only if no latent MVDs exist, and also give some results about this problem in the presence of latent MVDs.更多还原