Laura — a service-based coordination language

Open distributed systems are computing systems that can be characterized by a heterogeneity of involved machine- and network architectures as well as of the data processed. They have to be able to integrate existing applications, to cope with the use of multiple programming-languages, and potentially high dynamics by joining and leaving components. The coordination language Laura is designed to facilitate the use and offer of services in such a system. It is based on a shared collection of forms describing offers, requests, and results of services, called the service-space. Lauraʹs operations permit the exchange of forms via the service-space, guided by a matching-rule based on a subtype-notion on service types. The uncoupled coordination paradigm inherited from Linda allows it to meet the requirements of open systems. An architecture for a distributed Laura-system is described, that is scalable and can be adjusted to organizational borders. The architecture has been implemented on top of the ISIS toolkit. With Laura, we apply Lindaʹs coordination paradigm to open systems. Based on an analysis of the issue of names in open systems, we introduce a new approach to typing of interfaces. The architecture we propose includes new extensions to a partial replication scheme that can cope with dynamically changing set of participating machines.