A Generic Model for Persistence in (C)LP Systems

Abstract. This paper describes a model of persistence in (C)LP lan-guages and two di®erent ways to implement it in current systems. The fundamental idea is that persistence is a characteristic of certain dy-namic predicates which encapsulate state. The main e®ect of declaring a predicate persistent is that the dynamic changes made to such predi-cates survive from one execution to the next one. We propose a syntax for declaring persistent predicates and then a simple, ¯le-based imple-mentation is presented. It is then argued that the concept developed provides the most natural way to interface with relational databases. Such an interface is then developed as simply one more implementation alternative to the simple, ¯le-based approach. The abstraction of the concept of persistence from its implementation allows developing appli-cations which can store data alternatively on ¯les or databases with only a few simple changes to a declaration stating the location and modality used for persistent storage. Performance results comparing the di®erent implementations, and also with and without information obtained from static global analysis, is presented.