In a research and technology application project at Bellcore, we used multidatabase transactions to model multisystem work flows of telecommunication applications. During the project a prototype scheduler for executing multi-database transactions was developed. Two of the issues addressed in this project were concurrent execution of multi-database transactions and their failure recovery. This paper discusses our use of properties of the application and the telecommunication systems to develop simple and efficient solutions to the concurrency control and recovery problems.

The semantics L.0, a programming language designed for the specification and simulation of protocols that assumes a true concurrency model, is given in terms of predicate linear temporal logic, and the restricted universe of models assumed in L.0 programs is defined. The execution algorithm for L.0 constructs a model in this universe. The restricted subset of temporal logic exploited permits a nonbacktracking execution algorithm. Fundamental to the semantics of L.0 is a frame assumption, which generalizes the frame assumption of standard imperative programming, and which eases specification of protocols. The data domain assumed in L.0 programs is sets of trees with labeled edges, and the state predicates permitted include existence and nonexistence predicates, as well as the more traditional assignment and equality predicates. These choices for data domain and predicates permit convenient specification of the hierarchical message structure often assumed in telecommunications protocols, for in such message structures, the existence or nonexistence of parts of the message hierarchy is determined by logical properties of the rest of the message hierarchy. A small portion of the logical layer specification of Futurebus+ is taken as the main example in this study.>

A description is given of L.0, an executable specification language designed for describing communications protocols and similar reactive systems. L.0 is synchronous and rule-based. The rules are either cause-effect rules or constraints. Rules can be activated and deactivated dynamically, and several can be fired simultaneously. L.0 has modern notions of encapsulation and data sharing. Indirection, quantification, and recursive definition of modules increase its expressiveness. L.0 has been used in several development projects to design, simulate, and prototype protocols. It seems to provide a paradigm that is precise and yet can be used by designers and engineers who are not specialists in specification languages.>

The IC* project is an effort to create an environment for the design, specification, and development of complex systems such as communication protocols, parallel machines, and distributed systems. The basis of the project is the IC* model of parallel computation, in which a system is specified by a set of invariant expressions which describe its behavior in time. The features of this model include temporal and structural constraints, inherent parallelism, explicit modeling of time, nondeterministic evolution, and dynamic activation. The project also includes the construction of a parallel computer specifically designed to support the model of computation. The authors discuss the IC* model and the current user language, and describe the architecture and hardware of the prototype supercomputer built to execute IC* programs.>