We are investigating fundamental issues in providing systems support for ultradependable multiprocessor systems. The effort involves research in two interrelated areas: first, we are investigating software issues in the specification and implementation of dependable computing systems, and second, we are developing a prototype distributed, parallel computing environment to support robust concurrent applications. Our approach is to provide for separation of design concerns to support modular construction of highly robust concurrent computing systems. The project is developing linguistic and system support for combining user-level specification of performance and reliability requirements with architectural characteristics such as intercon- nect topology, message latency, bandwidth, and processor granularity.

Distributed databases can provide enhanced data availability to support applications such as office automation and computer-aided design and manufacturing. But first further work is needed on problems such as maintaining the consistency of replicated data in an efficient, reliable manner. We are attacking this and related problems by the development of provably correct, reliable protocols and by the analysis and simulation of competing protocols and algorithms.

From the aspect of supporting security, mobile computers have the benefit of only one user, irrespective of where and when the machine is used. However, the security benefits of a mobile computer are offset by several security problems. When communicating over networks with systems that implement secure channels, mobile computers must be able to establish and reestablish secure communication as they disconnect and reconnect. Current delegation schemes used in distributed systems are not well suited for disconnected operation. We are studying modifications to traditional delegation schemes that offers more flexibility and expressibility.

The system problems introduced by the wide-spread use of digital libraries involve many computer research concerns. They include disk and network I/O bottlenecks, distributed naming and addressing, load balancing, data migration, caching, data representations, disk layout, efficient object stores, scaling, security, access control, authentication, distributed directory structures and nameservers, distributed file systems, real-time data access, and protocols. The current and proposed digital library systems at UIUC allow us to investigate user characteristics, the performance load, and the performance behavior of various architectures supporting large digital libraries with many users.