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The programmer in a distributed processing environment must be provided with a set of facilities which permit easy specification of the distributive properties of his/her program. The word program here is used to refer to either the output of a single compilation or the output of independent compilations of program modules which are to be communicating via an IPC. These distributive properties include the specification of the concurrency, data flow, resource requirements (memory, devices, etc.), and intraprogram (intermodule) protocol properties inherent in the execution of a configuration (system) of cooperating software modules. Given a description of these properties, an operating system must be able to distribute the user's program across multiple machines in a manner which is transparent to the programmer. Traditional approaches to providing these facilities include the concurrency support in high-level languages and the resource allocation and concurrency support in conventional operating systems.

Viewgraphs on the topic of programming fault-tolerant distributed systems in the Ada programming language are presented. Topics covered include project goals, Ada difficulties and solutions, testbed requirements, and virtual processors.

We study one-dimensional integral inequalities, with quadratic integrands, on bounded domains. Conditions for these inequalities to hold are formulated in terms of function matrix inequalities which must hold in the domain of integration. For the case of polynomial function matrices, sufficient conditions for positivity of the matrix inequality and, therefore, for the integral inequalities are cast as semi-definite programs. The inequalities are used to study stability of linear partial differential equations.

ATC-NY and Cornell University are developing SCorES, a mathematically based tool to support the development of demonstrably correct distributed Systems. SCorES extends to distributed and hybrid systems a paradigm for program development that has been successful in the world of sequential programming-employing methods that are declarative (rather than operational) and constructive. Declarative methods permit systems to be specified, analyzed, developed, and verified at a conceptual level congenial to human designers. Constructive methods permit automatic code synthesis. Incorporating these methods within the NuPrl environment provides powerful automated support for specifying, developing, verifying, and synthesizing real-time distributed systems at a high level of abstraction. This report describes two things: a prototype that supports automatic code generation from proofs in a domain-specific logic of distributed systems (one that does not model real-time); an extension of that logic to the domain of hybrid systems, which may contain variables that vary continuously in real time. We demonstrate the code generator by deriving a verifiably correct leader election protocol; and we demonstrate the logic of hybrid systems by applying it to a mutual exclusion algorithm that generalizes Fischer's protocol to distributed systems.

ATC-NY and Cornell University are developing SCorES, a mathematically based tool to support the development of demonstrably correct distributed Systems. SCorES extends to distributed and hybrid systems a paradigm for program development that has been successful in the world of sequential programming-employing methods that are declarative (rather than operational) and constructive. Declarative methods permit systems to be specified, analyzed, developed, and verified at a conceptual level congenial to human designers. Constructive methods permit automatic code synthesis. Incorporating these methods within the NuPrl environment provides powerful automated support for specifying, developing, verifying, and synthesizing real-time distributed systems at a high level of abstraction. This report describes two things: a prototype that supports automatic code generation from proofs in a domain-specific logic of distributed systems (one that does not model real-time); an extension of that logic to the domain of hybrid systems, which may contain variables that vary continuously in real time. We demonstrate the code generator by deriving a verifiably correct leader election protocol; and we demonstrate the logic of hybrid systems by applying it to a mutual exclusion algorithm that generalizes Fischer's protocol to distributed systems.

The manual application of formal methods in system specification has produced successes, but in the end, despite any claims and assertions by practitioners, there is no provable relationship between a manually derived system specification or formal model and the customer's original requirements. Complex parallel and distributed system present the worst case implications for today s dearth of viable approaches for achieving system dependability. No avenue other than formal methods constitutes a serious contender for resolving the problem, and so recognition of requirements-based programming has come at a critical juncture. We describe a new, NASA-developed automated requirement-based programming method that can be applied to certain classes of systems, including complex parallel and distributed systems, to achieve a high degree of dependability.

Network programming language, dedicated for parallel programming in distributed systems based on ideology of multiprocessors with dynamic architecture (MDA) that provide automatic paralleling programs, high reliability of computations and unlimited scaling is considered. The language considered describes not the algorithm of the problem being solved but its initial structure that can be transformed during the process of solution. The language has two forms of program representation – graphic and text ones and completely releases the programmer from care of paralleling program and of computational resources used.

We developed StarL as a framework for programming, simulating, and verifying distributed systems that interacts with physical processes. StarL framework has (a) a collection of distributed primitives for coordination, such as mutual exclusion, registration and geocast that can be used to build sophisticated applications, (b) theory libraries for verifying StarL applications in the PVS theorem prover, and (c) an execution environment that can be used to deploy the applications on hardware or to execute them in a discrete event simulator. The primitives have (i) abstract, nondeterministic specifications in terms of invariants, and assume-guarantee style progress properties, (ii) implementations in Java/Android that always satisfy the invariants and attempt progress using best effort strategies. The PVS theories specify the invariant and progress properties of the primitives, and have to be appropriately instantiated and composed with the application's state machine to prove properties about the application. We have built two execution environments: one for deploying applications on Android/iRobot Create platform and a second one for simulating large instantiations of the applications in a discrete even simulator. The capabilities are illustrated with a StarL application for vehicle to vehicle coordination in a automatic intersection that uses primitives for point-to-point motion, mutual exclusion, and registration.

This is the final status report on the DoD-URIP grant for instrumentation to support research in distributed operating systems, fault-tolerant distributed computing, object-oriented computing and other related facets of distributed computing. The Distributed Systems Laboratory was established in the Computer Science Department of the University of Minnesota for this purpose. Currently this laboratory is supporting experimental research in the area fault-tolerant distributed operating systems, specifically to support development of the NEXUS distributed operating system. Currently this laboratory has a total of 12 workstations and 2 file servers with total storage capacity of 2 gigabytes. All these workstations are connected by an ethernet local area network that supports the Computer Science Department.

Modern distributed systems consisting of powerful workstations and high-speed interconnection networks are an economical alternative to special- purpose super computers. The technical issues that need to be addressed in exploiting the parallelism inherent in a distributed system include heterogeneity, high-latency communication, fault tolerance and dynamic load balancing. Current software systems for parallel programming provide little or no automatic support towards these issues and require users to be experts in fault-tolerant distributed computing. The Paralex system is aimed at exploring the extent to which the parallel application programmer can be liberated from the complexities of distributed systems. Paralex is a complete programming environment and makes extensive use of graphics to define, edit, execute and debug parallel scientific applications. All of the necessary code for distributing the computation across a network and replicating it to achieve fault tolerance and dynamic load balancing is automatically generated by the system. In this paper we give an overview of Paralex and present our experiences with a prototype implementation.

We describe a programming model called PTIDES (Programming Temporally Integrated Distributed Embedded Systems), that extends the discrete-event model of computation with a carefully chosen relationship between real time and model time. PTIDES provides a framework for exploring a family of execution strategies for distributed embedded systems. Our objective in this paper is to present an execution strategy that 1) allows independent events to be processed out of time stamp order, 2) uses clock synchronization as a replacement for null message communication across distributed platforms, 3) defines a notion of when events are safe to process and 4) presents an implementation of a PTIDES model. This work puts forward an execution strategy that is aggressive in concurrent execution of events.

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Distributed War Gaming (DWG) is the interactive simulation of military defense systems employing their command and control systems and the data processing capabilities of their headquarters. Using land-warfare as an example, a conceptual framework for the development of DWG information systems is provided which is based on the utilization of object-oriented software systems. In contrast to traditional software, these systems invoke the transformation of data by messages between objects which specify the transformation to be performed by the addressed object. When defining the system to be modelled, the analyst needs to be concerned with the reaction of individual objects to local messages only. The dynamics of complex systems are the results of the propagation of local messages to its individual elements. Based on a brief description of the basic principles behind object-oriented languages, a classification of objects and their attributes in a land-wargame is discussed and a definition of object behaviors is illustrated. Eight basic types of messages for a DWG and their formats are proposed, as is an algorithm for the synchronization of distributed simulations in DWG. Object-oriented software systems are judged to have potential for facilitating evolution in military software development. Their use in DWG could, in the long run, alleviate the problem of model acceptability. Thus, the development of prototype DWG-systems is proposed for feasibility testing and for the development of a strategy for the evolution of operational DWG-systems. (Author)

Distributed War Gaming (DWG) is the interactive simulation of military defense systems employing their command and control systems and the data processing capabilities of their headquarters. Using land-warfare as an example, a conceptual framework for the development of DWG information systems is provided which is based on the utilization of object-oriented software systems. In contrast to traditional software, these systems invoke the transformation of data by messages between objects which specify the transformation to be performed by the addressed object. When defining the system to be modelled, the analyst needs to be concerned with the reaction of individual objects to local messages only. The dynamics of complex systems are the results of the propagation of local messages to its individual elements. Based on a brief description of the basic principles behind object-oriented languages, a classification of objects and their attributes in a land-wargame is discussed and a definition of object behaviors is illustrated. Eight basic types of messages for a DWG and their formats are proposed, as is an algorithm for the synchronization of distributed simulations in DWG. Object-oriented software systems are judged to have potential for facilitating evolution in military software development. Their use in DWG could, in the long run, alleviate the problem of model acceptability. Thus, the development of prototype DWG-systems is proposed for feasibility testing and for the development of a strategy for the evolution of operational DWG-systems. (Author)

Distributed War Gaming (DWG) is the interactive simulation of military defense systems employing their command and control systems and the data processing capabilities of their headquarters. Using land-warfare as an example, a conceptual framework for the development of DWG information systems is provided which is based on the utilization of object-oriented software systems. In contrast to traditional software, these systems invoke the transformation of data by messages between objects which specify the transformation to be performed by the addressed object. When defining the system to be modelled, the analyst needs to be concerned with the reaction of individual objects to local messages only. The dynamics of complex systems are the results of the propagation of local messages to its individual elements. Based on a brief description of the basic principles behind object-oriented languages, a classification of objects and their attributes in a land-wargame is discussed and a definition of object behaviors is illustrated. Eight basic types of messages for a DWG and their formats are proposed, as is an algorithm for the synchronization of distributed simulations in DWG. Object-oriented software systems are judged to have potential for facilitating evolution in military software development. Their use in DWG could, in the long run, alleviate the problem of model acceptability. Thus, the development of prototype DWG-systems is proposed for feasibility testing and for the development of a strategy for the evolution of operational DWG-systems. (Author)

The manual application of formal methods in system specification has produced successes, but in the end, despite any claims and assertions by practitioners, there is no provable relationship between a manually derived system specification or formal model and the customer's original requirements. Complex parallel and distributed system present the worst case implications for today s dearth of viable approaches for achieving system dependability. No avenue other than formal methods constitutes a serious contender for resolving the problem, and so recognition of requirements-based programming has come at a critical juncture. We describe a new, NASA-developed automated requirement-based programming method that can be applied to certain classes of systems, including complex parallel and distributed systems, to achieve a high degree of dependability.

The authors consider loosely coupled distributed computing systems in which processes interact through shared resources which are modeled as bulletin boards. The first part of the paper formalizes the notion of consistent behavior when unreliable processes concurrently access a bulletin board. The remainder of the paper discusses software techniques for implementing consistent bulletin boards in a network of processors lacking shared memory. Applications for the approach range from asynchronous interprocess communication to mechanisms for achieving mutual exclusion, deadlock detection and for building distributed database systems.