Formal semantics of rights and confidentiality in definite deductive databases

We present a new approach to the definition of confidentiality in databases. It distinguishes itself by a well-founded formal semantics. We investigate the semantics of a database consequent upon the introduction of users and rights. Regarding a database with rights as a proper extension of an open database, we define the notion of global validity and that of a personal database profile. We identify conditions which guarantee that the introduction of rights and confidentiality requirements does not affect the database semantics. To create a more realistic situation, each user is assumed to have his own knowledge. We then give four new formal definitions of confidentiality, (G1) to (G4), which have been motivated by real-life situations. They correspond to the information contained in the informal answers `Maybe´, `No´, `Don´t know´ and `Don´t understand´ i.e., they capture the various degrees of implicit information a user may obtain on a secret. Three of them, (G1) for indefinite, (G2) for negative, and (G4) for zero-knowledge on secrets, prove relevant in the presence of the Closed World Assumption. The presented approach is theoretically sound and completely embodied in the standard predicate logic