Safe query languages for constraint databases

Abstract

In the database framework of Kanellakis et al. [1990] it was argued that constraint query languages should take constraint databases as input and give other constraint databases that use the same type of atomic constraints as output. This closed-form requirement has been difficult to realize in constraint query languages that contain the negation symbol. This paper describes a general approach to restricting constraint query languages with negation to safe subsets that contain only programs that are evaluable in closed-form on any valid constraint database input.