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A framework for rigorously specifying the behavior of concurrent systems is proposed. It is based on the view of a concurrent system as a collection of interacting processes but no assumptions are made about the mechanisms for process synchronization and communication. A formal language is described that permits the expression of a broad range of logical and timing dependencies.

Two testbed programming environments to support the evaluation of a large range of parallel architectures have been implemented under the program Parallel Implementation of Scientific Computing Environments (PISCES). The PISCES 1 environment was applied to two areas of aerospace interest: a sparse matrix iterative equation solver and a dynamic scene analysis system. Currently, the NICE/SPAR testbed system for structural analysis is being modified for parallel operation under PISCES 2; the PISCES 1 applications are also being adapted for PISCES 2. A new formal model of concurrent computation has been developed, based on the mathematical system known as H graph semantics together with a timed Petri net model of the parallel aspects of a system.

Two testbed programming environments to support the evaluation of a large range of parallel architectures have been implemented under the program Parallel Implementation of Scientific Computing Environments (PISCES). The PISCES 1 environment was applied to two areas of aerospace interest: a sparse matrix iterative equation solver and a dynamic scene analysis system. Currently, the NICE/SPAR testbed system for structural analysis is being modified for parallel operation under PISCES 2; the PISCES 1 applications are also being adapted for PISCES 2. A new formal model of concurrent computation has been developed, based on the mathematical system known as H graph semantics together with a timed Petri net model of the parallel aspects of a system.

Computing architectures are being assembled that extend concurrent engineering practices by providing more efficient execution and collaboration on distributed, heterogeneous computing networks. Built on the successes of initial architectures, requirements for a next-generation design computing infrastructure can be developed. These requirements concentrate on those needed by a designer in decision-making processes from product conception to recycling and can be categorized in two areas: design process and design information management. A designer both designs and executes design processes throughout design time to achieve better product and process capabilities while expanding fewer resources. In order to accomplish this, information, or more appropriately design knowledge, needs to be adequately managed during product and process decomposition as well as recomposition. A foundation has been laid that captures these requirements in a design architecture called DREAMS (Developing Robust Engineering Analysis Models and Specifications). In addition, a computing infrastructure, called IMAGE (Intelligent Multidisciplinary Aircraft Generation Environment), is being developed that satisfies design requirements defined in DREAMS and incorporates enabling computational technologies.

The main objective of this project was to develop new semantic theories and automated tools for real-time and probabilistic concurrent systems; that is, systems of coordinating processes that exhibit behavior of a probabilistic or statistical nature and which must meet real-time constraints. The main results achieved include a new semantic framework for reasoning about the relative reliability of probabilistic systems in different operating environments; an efficient algorithm for checking whether a specification of a real-time concurrent system satisfies a correctness property specified in a real-time temporal logic; and a new model of soft real-time systems that allows users to make rigorous statements about the likelihood with which systems are guaranteed to meet deadlines. A number of these results have been incorporated into the Concurrency Factory verification toolkit. In turn, the Factory has provided a platform for technology transfer with several Long Island companies, including Parker-Hannifin, Reuters America, and Northrop Grumman.

The object of our research is the codification of programming knowledge for the synthesis of concurrent programs. This final report presents the derivation of two concurrent algorithms: dynamic programming (for the class of problems that run in polynomial time on sequential machines) and array multiplication. Both derived concurrent versions run in linear time. The concurrent versions are significant and complex algorithms, though they are not new and already have been reported in the literature. The synthesis knowledge for these derivations is embodied in seven synthesis rules, preliminary versions of which are presented in this report. The rules will probably generalize to other classes of algorithms but we have not explored that issue yet. We have also discovered a pair of techniques called virtualization and aggregation. This pair of techniques (plus the other seven rules) is shown to be powerful enough to synthesize Kung's systolic array architecture (Kung-76) from a specification of matrix multiplication.

The object of our research is the codification of programming knowledge for the synthesis of concurrent programs. This final report presents the derivation of two concurrent algorithms: dynamic programming (for the class of problems that run in polynomial time on sequential machines) and array multiplication. Both derived concurrent versions run in linear time. The concurrent versions are significant and complex algorithms, though they are not new and already have been reported in the literature. The synthesis knowledge for these derivations is embodied in seven synthesis rules, preliminary versions of which are presented in this report. The rules will probably generalize to other classes of algorithms but we have not explored that issue yet. We have also discovered a pair of techniques called virtualization and aggregation. This pair of techniques (plus the other seven rules) is shown to be powerful enough to synthesize Kung's systolic array architecture (Kung-76) from a specification of matrix multiplication.

Diseases & disorders

Concurrent Engineering Centers (CECs) are specialized facilities with a goal of generating and maturing engineering designs by enabling rapid design iterations. This is accomplished by co-locating a team of experts (either physically or virtually) in a room with a narrow design goal and a limited timeline of a week or less. The systems engineer uses a model of the system to capture the relevant interfaces and manage the overall architecture. A single model that integrates other design information and modeling allows the entire team to visualize the concurrent activity and identify conflicts more efficiently, potentially resulting in a systems model that will continue to be used throughout the project lifecycle. Performing systems engineering using such a system model is the definition of model-based systems engineering (MBSE); therefore, CECs evolving their approach to incorporate advances in MBSE are more successful in reducing time and cost needed to meet study goals. This paper surveys space mission CECs that are in the middle of this evolution, and the authors share their experiences in order to promote discussion within the community.

We outline some conceptual challenges in extending the PCC paradigm to a concurrent and distributed setting, and sketch a generalized notion of module correctness based on viewing communication contracts as economic games. The model supports compositional reasoning about modular systems and is meant to apply not only to certification of executable code, but also of organizational workflows.

The feasibility of using hypercube-connected concurrent processor systems for problems in computational fluid dynamics is studied. Both explicit and implicit numerical methods are considered and several alternative implementations of these methods are evaluated on concurrent processor systems. A Lax-Wendroff explicit method was designed and implemented for the Navier-Stokes equations. The code runs on the Intel iPSC concurrent processor system. Tests of this code show that it is reasonably efficient. The Beam and Warming implicit factored method was designed and implemented for Berger's equation. Preliminary tests show that the efficiency of code is poor.

The economy of sustainable livestock relies on production and consumption of quality products in the market. The by-product should be evaluated technically for preparation, production practices and marketing endeavours for maintaining its yield and demand in the open market for attributes of livestock systems. To fulfil the attribute, there is requirement of a system consisting of high genetic material and high producing animals. Now a days, many scheme and experiment trials funded by central, or state government are carried out in different zones of India and abroad for identification of these traits. There is need to understand the failure of any product in market and their acceptance in the society. After seeking many efforts, the advantage and disadvantage of the specific product should be admired and taken in an account viz. its potential liabilities associated to global warming, resistance towards microbes and ethics towards the livestock and then may be further designed or inculcate in the manufacturing house for further production of the product. The product should be value added and varieties preferably to high and low income consumers.

This report describes the research effort directed towards the study of issues concerning concurrent systems. Specifically the report concentrates on the design, evaluation, and tuning of application programs on parallel architectures. Issues including mapping algorithms to architectures, and parallel programming support tools are discussed. It is recognized that the currently available concurrent system analysis tools are not adequate in determining the detail performance of the application programs on specific architectures. To remedy this shortcomming, we recommend the development of a multiprocessor trace-driven simulator. This simulator will be beneficial to the evaluation on the performance of the SDI battle management algorithms on specific concurrent systems.

This survey is organized as follows: Section 2 describes the syntax and semantics of the temporal logics that are used in this paper. Section 3 states the model checking problem and give an efficient algorithm for checking simple branching-time formulas. Section 4 discusses the issue of fairness and show how the algorithm of Section 3 can be extended to include fairness constraints. Section 5 demonstrates how the model checking algorithm can be used to debug a simple mutual exclusion program. Section 6 describes some alternative approaches for verifying systems of finite state concurrent process. The complexity of checking linear temporal logic formulas are analyzed and the techniques of Pnueli and Lichtenstein and Vardi and Wolper are outlined. Additional applications to circuit and protocol verification are discussed in Section 7. The paper concludes in Section 8 with a discussion of some of the important remaining research problems like the state explosion problem.

Formal verification for complex concurrent systems is a computationally intensive and, in some cases, intractable process. The complexity is an inherent part of the verification process due to the system complexity that is an exponential function of the sizes of its components. However, some properties can be enforced by automatically synchronizing the components, thus eliminating the need for verification. Moreover, the complexity of the analysis required to enforce the properties grows incrementally with addition of new components and properties that make the system complexity grow exponentially. The properties in question are the receptive safety properties, a subset of safety properties that can only be violated by component actions. The receptive safety properties represent the realizable subset of the general safety properties because a system that satisfies any non-receptive safety properties must satisfy related receptive safety properties. This implies that any system with realizable safety requirements can be described as a set of components and receptive safety properties that specify the component interaction that satisfies the requirements. We have developed a method that automatically synchronizes complex concurrent systems to enforce their receptive safety properties. Many non-safety and non-receptive properties can be represented using receptive safety properties, and automated synchronization can be used to enforce them.

Includes bibliographical references (p. 197-198) and index

Includes bibliographical references (p. 197-198) and index

Petri nets are presented as a technique for representing computer systems having asynchronous, concurrent operations. The structure of the nets are analyzed as a means of demonstrating the correctness of the modeled system. The execution of the petri net is considered as a stochastic process, allowing analysis of the model as a queueing network system by transforming the petri net into its stochastic equivalent net. It is shown that product form solutions for the state probabilities exist for the class of state machine decomposable nets but not for the more general class of consistent petri nets. Solutions for the corresponding open systems are derived by extending the petri net model to include arbitrary sources and sinks. (Author)

Petri nets are presented as a technique for representing computer systems having asynchronous, concurrent operations. The structure of the nets are analyzed as a means of demonstrating the correctness of the modeled system. The execution of the petri net is considered as a stochastic process, allowing analysis of the model as a queueing network system by transforming the petri net into its stochastic equivalent net. It is shown that product form solutions for the state probabilities exist for the class of state machine decomposable nets but not for the more general class of consistent petri nets. Solutions for the corresponding open systems are derived by extending the petri net model to include arbitrary sources and sinks. (Author)

ADA104054

This packet contains three papers from a symposium on feedback systems held at a conference on human resource development (HRD). The first paper, "The Role of Feedback in Management Development Training" (K. Peter Kuchinke), reports on a survey-based study that investigated the role of feedback in nine management development training settings in a British government agency. The results of the study suggest that participants sought information about their performance frequently and from a variety of sources and that the feedback-seeking is important in the process of management development training. The second paper, "A Five Phase Framework for Designing a Successful Multirater Feedback System" (Allan H. Church, Janine Waclawski) notes that there is a need in the literature for more attention to the factors involved in creating a successful feedback process. A five-phase framework for designing such a system is based on the classic organizational development consulting skills model and many years of practitioner experience with large-scale feedback-based applications in Fortune 100 organizations. The final paper, "An Evaluation of the Quality of 360-Degree Assessment Instruments" (Froukje Jellema, Adrie Visscher, Martin Mulder), presents a checklist of standards on the basis of which 360-degree employee evaluation instruments are examined. Four 360-degree assessment instruments also are examined. The papers contain reference sections.(KC)

This packet contains three papers from a symposium on feedback systems held at a conference on human resource development (HRD). The first paper, "The Role of Feedback in Management Development Training" (K. Peter Kuchinke), reports on a survey-based study that investigated the role of feedback in nine management development training settings in a British government agency. The results of the study suggest that participants sought information about their performance frequently and from a variety of sources and that the feedback-seeking is important in the process of management development training. The second paper, "A Five Phase Framework for Designing a Successful Multirater Feedback System" (Allan H. Church, Janine Waclawski) notes that there is a need in the literature for more attention to the factors involved in creating a successful feedback process. A five-phase framework for designing such a system is based on the classic organizational development consulting skills model and many years of practitioner experience with large-scale feedback-based applications in Fortune 100 organizations. The final paper, "An Evaluation of the Quality of 360-Degree Assessment Instruments" (Froukje Jellema, Adrie Visscher, Martin Mulder), presents a checklist of standards on the basis of which 360-degree employee evaluation instruments are examined. Four 360-degree assessment instruments also are examined. The papers contain reference sections.(KC)

Verification methodologies for real-time systems can be classified according to whether they are based on a continuous time model or a discrete time model. Continuous time often provides a more accurate model of physical reality, while discrete time can be more efficient to implement in an automatic verifier based on state exploration techniques. Choosing a model appears to require a compromise between efficiency and accuracy. We avoid this compromise by constructing discrete time models that are conservative approximations of appropriate continuous time models. Thus, if a system is verified to be correct in discrete time, then it is guaranteed to also be correct in continuous time. We also show that models with explicit simultaneity can be conservatively approximated by models with interleaving semantics.

The Best Manufacturing Practices (BMP) Program was established by the Navy in 1985 with the mission to collect, analyze and disseminate information on proven techniques used by the government and industry throughout the acquisition, development and field support process. Typically, this information is obtained via on-site surveys of a company's production lines and through meetings with development and production managers and personnel. The BMP Program has four main products: Best Practices Survey Reports, the Program Manager's Workstation (PMWS), WEB and Virtual Office services, and Systems Engineering work for Program Managers.

The Best Manufacturing Practices (BMP) Program was established by the Navy in 1985 with the mission to collect, analyze and disseminate information on proven techniques used by the government and industry throughout the acquisition, development and field support process. Typically, this information is obtained via on-site surveys of a company's production lines and through meetings with development and production managers and personnel. The BMP Program has four main products: Best Practices Survey Reports, the Program Manager's Workstation (PMWS), WEB and Virtual Office services, and Systems Engineering work for Program Managers.

Results are summarized for an investigation to assess the infrastructure available and the technology readiness in order to develop computational simulation methods/software for concurrent engineering. These results demonstrate that development of computational simulation methods for concurrent engineering is timely. Extensive infrastructure, in terms of multi-discipline simulation, component-specific simulation, system simulators, fabrication process simulation, and simulation of uncertainties--fundamental to develop such methods, is available. An approach is recommended which can be used to develop computational simulation methods for concurrent engineering of propulsion systems and systems in general. Benefits and issues needing early attention in the development are outlined.

The overall objective of this effort is to discover on-line fault detection, isolation and repair techniques and measures of effectiveness which will be ultimately applicable to tactical and strategic modular digital systems.

Volume 2-Computational Fluid dynamics and Wave Propagation; Parallel Computing; Concurrent and Supercomputing; Computational Physics/Computational Chemistry and Evolutionary Systems.

The complex digital electronic systems necessary for successfully attaining the SDIO mission will be composed of extremely large numbers of fine geometry active devices densely integrated with potentially submicron interconnect. A major problem with the integration of these complex microelectronic circuits on VLSI chips and wafer-scale integration is that they become highly susceptible to physical failures and environmental disturbances, especially intermittent and transient failures. This problem is aggravated when these electronic systems are deployed in harsh environments potentially resulting in erroneous computation due to transient failures as projected in the SDIO mission. Failures can result in disastrous incorrect computational results or complete system shutdown. The purpose of this research has been to develop techniques for the design of highly reliable electronic digital systems based on the concurrent detection of errors and rapid recovery from failures and environmentally induced upsets. Concurrent error detection consistently monitors the correctness of computational results and therefore allows for the detection of errors due to transient environmental upsets as well as permanent failures. Basic scientific results were obtained in this research concerning the derivation of design and analysis principles for concurrent error detection and recovery in electronic systems.

The complex digital electronic systems necessary for successfully attaining the SDIO mission will be composed of extremely large numbers of fine geometry active devices densely integrated with potentially submicron interconnect. A major problem with the integration of these complex microelectronic circuits on VLSI chips and wafer-scale integration is that they become highly susceptible to physical failures and environmental disturbances, especially intermittent and transient failures. This problem is aggravated when these electronic systems are deployed in harsh environments potentially resulting in erroneous computation due to transient failures as projected in the SDIO mission. Failures can result in disastrous incorrect computational results or complete system shutdown. The purpose of this research has been to develop techniques for the design of highly reliable electronic digital systems based on the concurrent detection of errors and rapid recovery from failures and environmentally induced upsets. Concurrent error detection consistently monitors the correctness of computational results and therefore allows for the detection of errors due to transient environmental upsets as well as permanent failures. Basic scientific results were obtained in this research concerning the derivation of design and analysis principles for concurrent error detection and recovery in electronic systems.

Under this contract, the MIT Media Laboratory explored state-of-the- art display techniques, together with interactive means, on the theme of advanced mapping displays for the commander. Achievements - including some world firsts - occurred in three major research areas: Enhanced Display Qualities, in particular: the readability of tactical maps through enhanced resolution, unique graphical techniques such as transparency, spatio-temporal trade-offs, and removal of spatio-temporal clutter; map usability, through readily-annotated large-format displays, and visualization of terrain through low-cost, real-time 3-D computer graphics techniques. Broadened User Actions, through multimodal natural dialogue via concurrent speech input, gesture and gaze. Advanced Input/ Output, in particular: synthetic terrain holography from mapping data, and the innovation and development of real-time holographic video; the extraction of range data from camera depth-of-field information, both to make likelihood estimates of scene structure, and to evaluate user expressive facial output.... Large Format Displays, Terrain Visualization, Dynamic Maps, Multi-Modal Interaction, Holographic Mapping.

The Army faces a number of personnel needs as it transforms to meet the challenges of today and the near future. To meet these challenges, the Army is seeking recommendations on predictor measures, in particular measures of non-cognitive attributes (e.g., interests, values, and temperament), that could be administered to enhance Soldier selection and classification decisions. The U. S. Army Research Institute for the Behavioral and Social Sciences (ARI) conducted a Concurrent Validation (CV) research effort to advance this objective. The objectives of this research were twofold: (1) to examine the value of using new, experimental predictor measures to select recruits into the Army; and (2) to investigate the potential of new, experimental predictor measures to enhance the classification of recruits into entry-level jobs. Criterion measures and experimental predictors were administered to 424 first-term Active Army Soldiers representing five military occupational specialties (MOS): (a) 11B Infantryman, (b) 19K Armor Crewman, (c) 25U Signal Support Systems Specialist, (d) 63B Light Wheeled Vehicle Mechanic, and (e) 68W Health Care Specialist. The value of the experimental predictor measures to enhance recruit selection and classification were examined. Overall, the results indicate that the experimental predictors show potential to increment the existing Armed Services Vocational Aptitude Battery (ASVAB) for the purposes of selecting recruits into the Army and classifying them into entry-level jobs.

A major part of debugging, testing, and analyzing a complex software system is understanding what is happening within the system at run-time. Some developers advocate running within a debugger to better understand the system at this level. Others embed logging statements, even in the form of hard-coded calls to print functions, throughout the code. These techniques are all general, rough forms of what we call system monitoring, and, while they have limited usefulness in simple, sequential systems, they are nearly useless in complex, concurrent ones. We propose a set of new mechanisms, collectively known as a monitoring system, for understanding such complex systems, and we describe an example implementation of such a system, called IDebug, for the Java programming language.

The global testing problem studied in this paper is to seek a definite answer to whether a system of concurrent black-boxes has an observable behavior in a given finite (but could be huge) set "Bad". We introduce a novel approach to solve the problem that does not require integration testing. Instead, in our approach, the global testing problem is reduced to testing individual black-boxes in the system one by one in some given order. Using an automata-theoretic approach, test sequences for each individual black-box are generated from the system's description as well as the test results of black-boxes prior to this black-box in the given order. In contrast to the conventional compositional/modular verification/testing approaches, our approach is essentially decompositional. Also, our technique is complete, sound, and can be carried out automatically. Our experiment results show that the total number of tests needed to solve the global testing problem is substantially small even for an extremely large "Bad".

Petri nets are presented as a technique for representing computer systems having asynchronous, concurrent operations. The structure of the nets are analyzed as a means of demonstrating the correctness of the modeled system. The execution of the petri net is considered as a stochastic process, allowing analysis of the model as a queueing network system by transforming the petri net into its stochastic equivalent net. It is shown that product form solutions for the state probabilities exist for the class of state machine decomposable nets but not for the more general class of consistent petri nets. Solutions for the corresponding open systems are derived by extending the petri net model to include arbitrary sources and sinks. (Author)

At its inception, this project was designed to represent a comprehensive program of research in the field of distributed database management. The problems to be dealt with were to include the three major topics in distributed database: query processing, concurrency control and crash recovery. In addition, the problem of interconnecting heterogeneous databases was also proposed. To a substantial extent, major progress has been achieved in all these areas. In this report a summary of the principal findings is presented.

At its inception, this project was designed to represent a comprehensive program of research in the field of distributed database management. The problems to be dealt with were to include the three major topics in distributed database: query processing, concurrency control and crash recovery. In addition, the problem of interconnecting heterogeneous databases was also proposed. To a substantial extent, major progress has been achieved in all these areas. In this report a summary of the principal findings is presented.

In this paper, we extend the theory CCS for trees (CCTS) to value-passing CCTS (VCCTS), of which symbols have the capacity for receiving and sending data values, and a nonsequential semantics is proposed in an operational approach. In this concurrent model, a weak barbed congruence and a localized early weak bisimilarity are defined, and the latter relation is proved to be sufficient to justify the former. As an illustration of potential applications of VCCTS, a semantics based on VCCTS is given to a toy multi-threaded programming language featuring a core of C/C++ concurrency; and a formalization based on the operational semantics of VCCTS is proposed for some relaxed memory models, and a DRF-guarantee property with respect to VCCTS is proved.

Established at the NASA Glenn Research Center (GRC) in 2006 to meet the need for rapid mission analysis and multi-disciplinary systems design for in-space and human missions, the Collaborative Modeling for Parametric Assessment of Space Systems (COMPASS) team is a multidisciplinary, concurrent engineering group whose primary purpose is to perform integrated systems analysis, but it is also capable of designing any system that involves one or more of the disciplines present in the team. The authors were involved in the development of the COMPASS team and its design process, and are continuously making refinements and enhancements. The team was unofficially started in the early 2000s as part of the distributed team known as Team JIMO (Jupiter Icy Moons Orbiter) in support of the multi-center collaborative JIMO spacecraft design during Project Prometheus. This paper documents the origins of a concurrent mission and systems design team at GRC and how it evolved into the COMPASS team, including defining the process, gathering the team and tools, building the facility, and performing studies.

Concurrent Engineering Centers (CECs) are specialized facilities with a goal of generating and maturing engineering designs by enabling rapid design iterations. This is accomplished by co-locating a team of experts (either physically or virtually) in a room with a focused design goal and a limited timeline of a week or less. The systems engineer uses a model of the system to capture the relevant interfaces and manage the overall architecture. A single model that integrates other design information and modeling allows the entire team to visualize the concurrent activity and identify conflicts more efficiently, potentially resulting in a systems model that will continue to be used throughout the project lifecycle. Performing systems engineering using such a system model is the definition of model-based systems engineering (MBSE); therefore, CECs evolving their approach to incorporate advances in MBSE are more successful in reducing time and cost needed to meet study goals. This paper surveys space mission CECs that are in the middle of this evolution, and the authors share their experiences in order to promote discussion within the community.

The spring 2001 issue of "New Directions for Community Colleges" discusses concurrent enrollment programs and the challenges and issues associated with developing and maintaining such programs. Chapters include: (1) "State Policy and Postsecondary Enrollment Options: Creating Seamless Systems" (Katherine Boswell); (2) "A Model for Implementing a Concurrent Enrollment Program" (Brian G. Chapman); (3) "Designing an Effective Concurrent Enrollment Program: A Focus on Quality of Instruction and Student Outcomes" (Margaret K. Peterson, John Anjewierden, and Cris Corser); (4) "Concurrent Enrollment in Arizona: Encouraging Success in High School" (Donald E. Puyear, Linda M. Thor, and Karen L. Mills); (5) "Concurrent Enrollment and More: Elements of a Successful Partnership" (Steven R. Helfgot); (6) "Dual Enrollment in Virginia" (Rhonda K. Catron); (7) "New World School of the Arts: Creativity Across the Curriculum" (Nancy M. Wolcott); (8) "Dual Enrollment for Underrepresented Student Populations" (Esther B. Hugo); (9) "Dual Enrollment Options: Columbus State Community College Model for Successful Implementation" (Tammi C. Jordan); and (10) "Sources and Information: Creating Effective Collaboration Between High Schools and Community Colleges" (Gigi G. Gomez). (EMH)

The paradigm shift from inherently sequential to highly concurrent and multi-threaded applications is creating new challenges for testers and verification engineers. In this work we present an abstraction-guided hybrid symbolic execution technique to check the reachability of certain target locations. The input target locations are generated from static analysis warnings or user-specified reachability properties. We generate an abstract system that contains program locations relevant for checking the reachability of the target locations. We guide a hybrid symbolic program execution (data input values are represented symbolically while other values are concrete) along paths in the abstract system in order to generate a corresponding feasible execution trace. We use a combination of heuristics for ranking thread and data non-determinism to guide the execution. An empirical analysis demonstrates that abstract traces can quickly be concretized to find concurrency errors using the guided hybrid symbolic execution technique where exhaustive search techniques fail. ©2009 Microsoft Corporation. All rights reserved.

We study algorithmic questions for concurrent systems where the transitions are labeled from a complete, closed semiring, and path properties are algebraic with semiring operations. The algebraic path properties can model dataflow analysis problems, the shortest path problem, and many other natural problems that arise in program analysis. We consider that each component of the concurrent system is a graph with constant treewidth, a property satisfied by the controlflow graphs of most programs. We allow for multiple possible queries, which arise naturally in demand driven dataflow analysis. The study of multiple queries allows us to consider the tradeoff between the resource usage of the one-time preprocessing and for each individual query. The traditional approach constructs the product graph of all components and applies the best-known graph algorithm on the product. In this approach, even the answer to a single query requires the transitive closure, which provides no room for tradeoff between preprocessing and query time. Our main contributions are algorithms that significantly improve the worst-case running time of the traditional approach, and provide various tradeoffs depending on the number of queries. For example, in a concurrent system of two components, the traditional approach requires hexic time in the worst case for answering one query as well as computing the transitive closure, whereas we show that with one-time preprocessing in almost cubic time, each subsequent query can be answered in at most linear time, and even the transitive closure can be computed in almost quartic time. Furthermore, we establish conditional optimality results showing that the worst-case running time of our algorithms cannot be improved without achieving major breakthroughs in graph algorithms.

From the bitsavers.org collection, a scanned-in computer-related document. mitre :: ESD Technical Reports :: ESD-TR-71-221 Concurrent Data Sharing Problems In Multiple User Computer Systems Jul71

Compositionality and process equivalence are both standard concepts of process algebra. Compositionality means that the behaviour of a compound system relies only on the behaviour of its components, i.e. there is no emergent behaviour. Process equivalence means that the explicit statespace of a system takes a back seat to its interaction patterns: the information that an environment can obtain though interaction. Petri nets are a classical, yet widely used and understood, model of concurrency. Nevertheless, they have often been described as a non-compositional model, and tools tend to deal with monolithic, globally-specified models. This tutorial paper concentrates on Petri Nets with Boundaries (PNB): a compositional, graphical algebra of 1-safe nets, and its applications to reachability checking within the tool Penrose. The algorithms feature the use of compositionality and process equivalence, a powerful combination that can be harnessed to improve the performance of checking reachability and coverability in several common examples where Petri nets model realistic concurrent systems.

Compositionality and process equivalence are both standard concepts of process algebra. Compositionality means that the behaviour of a compound system relies only on the behaviour of its components, i.e. there is no emergent behaviour. Process equivalence means that the explicit statespace of a system takes a back seat to its interaction patterns: the information that an environment can obtain though interaction. Petri nets are a classical, yet widely used and understood, model of concurrency. Nevertheless, they have often been described as a non-compositional model, and tools tend to deal with monolithic, globally-specified models. This tutorial paper concentrates on Petri Nets with Boundaries (PNB): a compositional, graphical algebra of 1-safe nets, and its applications to reachability checking within the tool Penrose. The algorithms feature the use of compositionality and process equivalence, a powerful combination that can be harnessed to improve the performance of checking reachability and coverability in several common examples where Petri nets model realistic concurrent systems.

Compositionality and process equivalence are both standard concepts of process algebra. Compositionality means that the behaviour of a compound system relies only on the behaviour of its components, i.e. there is no emergent behaviour. Process equivalence means that the explicit statespace of a system takes a back seat to its interaction patterns: the information that an environment can obtain though interaction. Petri nets are a classical, yet widely used and understood, model of concurrency. Nevertheless, they have often been described as a non-compositional model, and tools tend to deal with monolithic, globally-specified models. This tutorial paper concentrates on Petri Nets with Boundaries (PNB): a compositional, graphical algebra of 1-safe nets, and its applications to reachability checking within the tool Penrose. The algorithms feature the use of compositionality and process equivalence, a powerful combination that can be harnessed to improve the performance of checking reachability and coverability in several common examples where Petri nets model realistic concurrent systems.

Petri nets are presented as a technique for representing computer systems having asynchronous, concurrent operations. The structure of the nets are analyzed as a means of demonstrating the correctness of the modeled system. The execution of the petri net is considered as a stochastic process, allowing analysis of the model as a queueing network system by transforming the petri net into its stochastic equivalent net. It is shown that product form solutions for the state probabilities exist for the class of state machine decomposable nets but not for the more general class of consistent petri nets. Solutions for the corresponding open systems are derived by extending the petri net model to include arbitrary sources and sinks. (Author)

Petri nets are presented as a technique for representing computer systems having asynchronous, concurrent operations. The structure of the nets are analyzed as a means of demonstrating the correctness of the modeled system. The execution of the petri net is considered as a stochastic process, allowing analysis of the model as a queueing network system by transforming the petri net into its stochastic equivalent net. It is shown that product form solutions for the state probabilities exist for the class of state machine decomposable nets but not for the more general class of consistent petri nets. Solutions for the corresponding open systems are derived by extending the petri net model to include arbitrary sources and sinks. (Author)