Thémis: A database programming language handling integrity constraints

Abstract

This article presents a database programming language, Thémis, which supports subtyping and class hierarchies, and allows for the definition of integrity constraints in a global and declarative way. We first describe the salient features of the language: types, names, classes, integrity constraints (including methods), and transactions. The inclusion of methods into integrity constraints allows an increase of the declarative power of these constraints. Indeed, the information needed to define a constraint is not always stored in the database through attributes, but is sometimes computed or derived data. Then, we address the problem of efficiently checking constraints. More specifically, we consider two different problems: (1) statically reducing the number of constraints to be checked, and (2) generating an efficient run-time checker. Using simple strategies, one can significantly improve the efficiency of the verification. We show how to reduce the number of constraints to be checked by characterizing the portions of the database that are involved in both the constraints and in a transaction. We also show how to generate efficient algorithms for checking a large class of constraints. We show how all the techniques presented exploit the underlying type system, which provides significant help in solving (1) and (2). Last, the current status of the Thémis prototype is presented.