Object-oriented database evolution

Abstract

An evolution languageis composed of an instance update language, a schema update language, and a mechanism to combine them. We present a formal evolution language for object-oriented database management systems. This language allows to write programs to update simultaneously both the schema and the instance. Static checking of these programs insures that the resulting database is consistent. We propose an autonomous instance update language, based on an adequate specific query language and a pure instance update language. The main features of the query language are a formal type inference system including disjunctive types, and the decidability of the satisfiability problem, despite a negation operator. The pure instance update language allows objects migration, and objects and references creation and deletion; its semantics is declarative, and an algorithm to compute it is presented. We propose an evolution mechanism for combining this instance update language with a classical schema update language, and use it to obtain an evolution language. Decidability of consistency is shown for a fragment of this language, by reduction to first-order logic with two variables.