ON THE POWER OF LANGUAGES FOR THE MANIPULATION OF COMPLEX VALUES y

Various models and languages for describing and manipulating hierarchically structured data have been proposed. Algebraic, calculus-based and logic-programming oriented languages have all been considered. This paper presents a general model for complex values (i.e., values with hierarchical structures), and languages for it based on the three paradigms. The algebraic language generalizes those presented in the literature; it is shown to be related to the functional style of programming advocated by Backus. The notion of domain independence familiar from relational databases is deened, and syntactic restrictions (referred to as safety conditions) on calculus queries are formulated, that guarantee domain independence. The main results are: The domain-independent calculus, the safe calculus, the algebra, and the logic-programming oriented language have equivalent expressive power. In particular , recursive queries, such as the transitive closure, can be expressed in each of the languages. For this result, the algebra needs the powerset operation. A more restricted version of safety is presented, such that the restricted safe calculus is equivalent to the algebra without the powerset. The results are extended to the case where arbitrary functions and predicates are used in the languages.Israelienne pour la Recherche Scientiique et Technologique. y Our main technical results have been included in an INRIA Technical Report 2], extensively revised in 1992. The major changes were an emphasis on the approach to extending existing languages to new models, a cleaner and simpler algebra, and simpler and better structured proofs of the major results. The current version is a minor improvement on the 1992 version.