ECOOP '91 is the fifth annual European Conference on Object-Oriented Programming. From their beginning, the ECOOP conferences have been very successful as a forum of high scientific quality where the newest devel- opments connected to object-oriented programming and related areas could be presented and discussed. Over the last few years object-oriented technology has gained widespread use and considerable popularity. In parallel with this, the field has matured scientifically, but there is still a lot of room for new ideas and for hot debates over fundamental issues, as these proceedings show. The 22 papers in this volume were selected by the programme committee from 129 submissions. Important issues discussed in the contributions are language design, specification, databases, concurrency types and software development.

This volume presents the proceedings of a workshop on parallel database systems organized by the PRISMA (Parallel Inference and Storage Machine) project. The invited contributions by internationally recognized experts give a thorough survey of several aspects of parallel database systems. The second part of the volume gives an in-depth overview of the PRISMA system. This system is based on a parallel machine, where the individual processors each have their own local memory and communicate with each other over a packet-switched network. On this machine a parallel object-oriented programming language, POOL-X, has been implemented, which provides dedicated support for database systems as well as general facilities for parallel programming. The POOL-X system then serves as a platform for a complete relational main-memory database management system, which uses the parallelism of the machine to speed up significantly the execution of database queries. The presentation of the PRISMA system, together with the invited papers, gives a broad overview of the state of the art in parallel database systems.