This paper discusses problems and confusion that can arise in normalizing certain relations, using the commonly accepted practices of identifying primary keys and defining normal forms. Specifically, normalization of relations that combines information on two different entities with a one-to-one relationship is discussed. It is shown that for such relations, using the standard normalization procedures may lead to the conclusion that a relation in Boyce-Codd normal form (BCNF) still suffers from insertion and deletion anomalies. Methods to deal with such cases are presented.
Philip, George, "Normalizing Relations: One-to-One Relationships" (1998). AMCIS 1998 Proceedings. 323.