Software services and software maintenance.

Software services are being promoted as the next big step forward in software engineering. Inevitably, both service vendor and service client programs will require maintenance. We present a service architecture that has been motivated by a long term vision for software as something which is used, not owned. This architecture is used to show how evolution of software can be achieved. It uses the marketplace to drive the process incrementally. We summarise a new fault-tolerant private information retrieval scheme for protecting users' privacy and ensuring service provision even in the presence of intentional/unintentional service provider faults (e.g. malicious failures). An implementation on a realistic distributed database suggests only a modest performance overhead