Optimizing Queries with Object Updates

Abstract

Object-oriented databases (OODBs) provide powerful data abstractions and modeling facilities but they usually lack a suitable framework for query processing and optimization. Even though there is an increasing number of recent proposals on OODB query optimization, only few of them are actually focused on query optimization in the presence of object identity and destructive updates, features often supported by most realistic OODB languages. This paper presents a formal framework for optimizing object-oriented queries in the presence of side effects. These queries may contain object updates at any place and in any form. We present a language extension to the monoid comprehension calculus to express these object-oriented features and we give a formal meaning to these extensions. Our method is based on denotational semantics, which is often used to give a formal meaning to imperative programming languages. The semantics of our language extensions is expressed in terms of our monoid calculus, without the need of any fundamental change to our basic framework. Our method not only maintains referential transparency, which allows us to do meaningful query optimization, but it is also practical for optimizing OODB queries since it allows the same optimization techniques applied to regular queries to be used with minimal changes for OODB queries with updates.