Discrete event system specification (DEVS) has been widely used within modeling and simulation to design, verify, and implement complex reactive systems. DEVS provides a robust formalism for designing systems using event-driven, state-based models in which timing information is explicitly defined. In this paper, we present an overview of a DEVS-based hardware design, synthesis, and optimization methodology. Within this approach, hardware DEVS (HDEVS) specifications can be synthesized to hardware, during which the event-driven model and explicit timing allow for an efficient hardware realization using globally asynchronous, locally synchronous design approach. Additionally, we present an optimization method for reducing power consumption through optimal frequency mapping and clock gating of individual components while ensuring system latency constraints are achieved. We further demonstrate the resulting power consumption savings for activity-driven forest fire and asthma health management applications targeting two low-power FPGA devices.

The recent development in cloud computing and Web service delivery encouraged companies from different disciplines to offer their services to customers over the Internet. Since different domains use different language of encounter to establish their contracts, a generic negotiation framework that can be tailored to a specific domain is needed. In this paper, we will present a generic domain-independent marketplace architecture that allows user agents to interact with service providers using two simple and yet powerful negotiation protocols. Service providers have different capabilities depending on the domain of interest. Hence, a dynamic message structuring capability is needed. A key solution to support expressive power is to design an ontology that contains specializations between different domains. The Integration of the domain-dependent ontology with the domain-independent marketplace gives the designer a powerful tool in which systems can be tailored based on the operational purpose. We demonstrate a proof of the concept by implementing the negotiation framework using Discrete Event Specification/Service Oriented Architecture (DEVS/SOA) environment.

This paper shows how to generate a finite-vertex graph, called a reachability graph for discrete-event system specification (DEVS) network. The reachability graph is isomorphic to a given original DEVS network in terms of behavior but the number of vertices as well as the number of edges of the reachability graph are finite.

This paper describes a method for creating synthetic air tracks without the aide of a sophisticated simulator. The proposed method creates a position and velocity function for an aircraft given its starting location and speed, altitude, and heading on each leg of its height. An optimization procedure is used to fit the position and velocity functions to the supplied data. Several examples of tracks produced by the method are shown in the paper. The synthetic tracks that are produced by this method can be used to facilitate testing of command and control systems and to enhance any simulation that requires air tracks that satisfy specific constraints on time, speed, and position.

QoS-aware service management and composition has become an interesting research topic with the rapid development of service oriented architecture (SOA). Differently with Web-services based systems, the emergence of peer-to-peer (P2P) based distributed network technology brings more challenge to the QoS-aware service management and composition. In this paper, we propose our design of a QoS-aware hierarchical service composition and management system in a context of JXTA-enabled P2P network. We conducted a comparison experiment of our design with commonly used flat-based service composition and management, and found that our design outperforms the flat-based one in terms of a higher success rate for satisfying the user's QoS requirement. Furthermore, we used a RT-DEVS model based formal approach to validate our design, and believe that it can be a promising technology in aiding the design of an efficient QoS-aware service composition and management system.

In this paper, we specialize the concept of "activity", defined in earlier work, to measure the heterogeneity of model behavior using the temporal- spatial distribution of its local transitions in a 2D cellular space. We then show how to employ this "activity" metric to balance the computation load using the dynamic reconfiguration of the distributed simulation. We also show how the degree of improvement depends on the heterogeneity of the activity's distribution. That is, high concentrations of activity in space that change relatively slowly during simulation can be exploited to reduce execution time significantly within an appropriate infrastructure for dynamic reconfiguration in a DEVS based distributed simulation framework. In contrast to other dynamic load balancing approaches, the activity-based approach discussed here exploits model properties directly rather than relying on resource-based measurements as the basis for its reconfigurations.

This paper presents the results of applying an incremental simulation-based design process to study a robotic convoy system. Robot-in-the-loop simulation, as a major step in this process, allows the system to be measured with combined robot models and real robots. This capability effectively bridges the gap between conventional simulation where models are used and real system experiment where real robots are used. For each step in this incremental process, the simulation/experiment setup is described. The measurement data are then presented and compared. These experiments and results demonstrate the capabilities of robot-in-the-loop simulation and justify the effectiveness of using the incremental simulation-based design process.

Complex spatially-extended systems consist of numerous sub-systems leading to large simulation execution times. One approach to reducing these execution times is designing a simulation engine to allocate its attention to subsystems in proportion to their activity levels. In this paper, we consider a large scale simulation of a physics-based fire spread model. This model is discretized using a recently developed numerical method called quantization and implemented using discrete event simulation. In this paper, we provide comparisons between the quantization method and usual Euler discrete-time methods. The aim is to demonstrate the ability of quantization and discrete event simulation to focus on active sub-systems, thus significantly reducing execution time for large heterogeneous systems.

A recent DoD mandate requires that the DoD architectural framework (DoDAF) be adopted to express high level system and operational requirements and architectures. DoDAF is the basis for integrated architectures and provides broad levels of specification related to operational, system, and technical views. The combination of DoDAF operational views, which capture the requirements of the architecture, and system views which provide its technical attributes, forms the basis for semi-automated construction of the needed simulation models. In this paper, we describe an approach to support specification of DoDAF architectures within a development environment based on DEVS (discrete event system specification). The result is an enhanced system lifecycle development process that includes both development and testing in an integral manner. This paper discusses the motivation to carve out a methodology to develop DEVS models for any DoDAF-UML architecture specifications and empower DoDAF with integrated M&S.

Model continuity refers to the ability to transition as much as possible a model specification through the stages of a development process. In this paper, the authors show how a modeling and simulation environment, based on the discrete event system specification formalism, can support model continuity in the design of dynamic distributed real-time systems. In designing such systems, the authors restrict such continuity to the models that implement the system's real-time control and dynamic reconfiguration. The proposed methodology supports systematic modeling of dynamic systems and adopts simulation-based tests for distributed real-time software. Model continuity is emphasized during the entire process of software development $the control models of a dynamic distributed real-time system can be designed, analyzed, and tested by simulation methods, and then smoothly transitioned from simulation to distributed execution. A dynamic team formation distributed robotic system is presented as an example to show how model continuity methodology effectively manages the complexity of developing and testing the control software for this system.

An approach to modeling and simulating distributed object computing systems as a set of software components mapped onto a set of networked processing nodes is presented. The modeling approach has clearly separated hardware and software components enabling systems level, distributed codesign engineering. The distributed codesign engineering refers to a system-theoretic approach to concurrent hardware and software systems engineering that provides a tractable method for analyzing the inherent complexities that arise in distributed computing systems. A software abstraction forms a distributed cooperative object (DCO) model to represent interacting software objects. A hardware abstraction forms a loosely coupled network (LCN) model of processing nodes, network gates and interconnecting communication links. The distribution of DCO software across LCN processors forms an object system mapping (OSM). This OSM provides a sufficient specification to allow simulation investigations. In simulation, the behavioral dynamics of the interacting DCO software components load and compete for LCN processing and networking resources. The LCN resource constraints thus impose performance constraints on the interactions of the DCO software objects. Class models of the DCO, LCN, and OSM component structures and behavior dynamics were formally characterized using the discrete event system specification (DEVs) formalism. These class model specifications were implemented in DEVSJAVA, a Java implementation of DEVS. Class models of experimental frame components were developed and implemented to facilitate analysis of the interdependent distributed system behaviors during simulations. Our DEVS-DOC M&S environment enables distributed systems architects, integration engineers and system designers to analyze performance and examine engineering trades of system structures, topologies and technologies. A case study demonstrates the ability to model and simulate a real world system and the complex interactions that arise in distributed computing systems.

In this paper the design and implementation of Distributed Real-Time DEVS/CORBA is discussed as an extension of previously developed DEVS-based modeling and simulation frameworks. The major objective in developing Distributed Real-Time DEVS/CORBA is to establish a framework in which the distributed real-time systems can be designed through DEVS-based modeling and simulation studies, and then migrated with minimal additional effort to be executed in the real-time distributed environment. This environment will provide generic support for developing models of distributed embedded software systems, evaluating their performance and timing behavior through simulation and easing the transition from simulation to actual executions In this paper we describe detailed design and implementation aspects of the environment which was implemented over Visibroier CORBA middleware and ACE/TAO real-time CORBA services.

This paper describes our effort to implement DEVS on a TINI Chip which has limited memory and processing ability. A set of well-defined DEVS interfaces make it possible to define a just-as-needed DEVS real time environment and run on the chip efficiently. As a case study for real time data gathering, processing and management, a DEVS coupled model has been composed from a set of primitive DEVS atomic models in this application area. This coupled model gets real time temperature from a sensor and runs data processing such as quantizer, moving averager, maximum and minimum extractor, etc. before it transfers the data to database.

This paper describes the design and development of DEVS/GDDM, an environmental platform for data distribution management, that allows us to study the interestbased quantization scheme in order to achieve effective reduction of data communication in distributed simulation. After a brief review of interest-based quantization scheme, we discuss the implementation of this scheme as a layer above the DEVS/HLA modeling and simulation environment. This paper presents theoretical analysis for bandwidth utilization of the interest-based quantization scheme, especially with predictive and multiplexing extensions, and empirical results in ballistic missiles simulation executing on the DEVS/GDDM environment in NT networking platforms. The results indicate that the DEVS/GDDM environment is very effective and scalable due to reduced local computation demands and extremely favorable communication data reduction with a reasonably small potential for error.

In this paper, we present two specifications, scalable DEVS specification and distributed container object specification, to support scalability and interoperability of DEVS-based modeling and simulation (M and S) systems. The scalable DEVS specification lists a set of interfaces which create and simulate DEVS models, and control simulation activities among simulators. The distributed container object specification provides a heterogeneous and distributed collection framework focusing on ensemble operations. The proposed specifications contain a rich set of both data and operations which are necessary for building scalable M and S environments that should provide invariance in both performance and quality of service of a system as the size, complexity, and interdependence of its elements increases. We describe design and implementation aspects of those specifications.

The paper proposes a layered architectural framework to support agent based system development in a collaborative, multidisciplinary engineering setting. This architecture is viewed from two distinct perspectives. First, the environment must enable agent based modeling and simulation. Second, it should support concurrent (team oriented) engineering. The main focus is on the proposed layered architecture delineating various needs of an agent based system, thus supporting incremental specification design, implementation, and testing. In our discussions, we distinguish between performing agents and simulated agents. The former refers to agents as they are performing their tasks in real-world settings. The latter refers to agents that have their behavior simulated in a virtual environment. In these terms, the proposed framework is intended to form the basis for environments that support development of agents, in both performance and simulation modes, as well as in hybrid combination (both performing and simulated agents interacting at the same time). The proposed framework is a step toward realization of agent based systems under the umbrella of the simulation based acquisition (SBA) initiative of the US Department of Defense.

Perceiving agents have a limited sensitivity to distinguish input stimuli. Whatever the cause random noise, limited numbers of sensing elements, intentional desensitization formulation of such behavioral phenomena at the system level has not attracted much interest. This work is a first attempt to formalize the limited-sensitivity abstraction and to explore its implications for systems modeling and simulation, both conceptual and practical. In this article, a system theoretic formalization of perceiving agents called quantized systems is provided, linking them with discrete event modeling paradigms and exploring their approximation capability and message reduction in distributed simulation.

Telemedicine remote consultation and diagnosis (RCD) software is a complex and distributed system. RCD allows physicians to collaborate on radiology or pathology cases from distributed geographic locations. It is very important to simplify design, construction, and maintenance of such a system. Currently, object-oriented design methodology is used to design and develop a software system in a modular fashion. Object-oriented software is made of various objects that work together. From the design of the software system, we get information about object methods and inheritance. We also get information about which objects are contained in a particular object and which objects are used by another object. One important element that the traditional object-oriented design misses is time. We propose the use of discrete event system specification (DEVS) in the design and analysis of a software system, such as RCD. With DEVS, coupling between objects can be specified explicitly and an object behavior can be shown in time. We introduce DEVS, show the time-line analysis of Remote Consultation and Diagnosis session playback using DEVS, and then describe its implementation.

We present an approach to embedding expert systems within an object-oriented simulation environment that facilitates the creation of classes of expert system model elements that can be interfaced with other model components. Previous work has shown how distributed expert systems can be defined as modular components of simulations models. This article illustrates their usefulness in fractal architectures for flexible manufacturing, as proposed in the literature. Alternate structures (reconfigured structures) of a proposed hierarchical factory architecture can be generated through the recursive pruning process. Such rapid prototyping should greatly enhance the ability to investigate alternative architectural solutions to manufacturing problems in a timely manner.

A multiresolutional search paradigm is employed to design optimal fuzzy logic controllers in a variable structure simulation environment. The initial search space is evaluated with a coarse resolution and some of the subspaces are selected as candidate regions for global optimum. New optimization processes are then created to investigate the candidate search spaces in detail, a process which continues until a solution is found. This search paradigm was implemented using hierarchical distributed genetic algorithms (HDGAs)-search agents solving different degrees of abstracted problems. Creation/destruction of agents is executed dynamically during the operation based on their performance. In the application to fuzzy systems, the HDGA investigates design alternatives such as different types of membership functions and the number of the fuzzy labels, as well as their optimal parameter settings, all at the same time. This paradigm is demonstrated with an application to the design of a fuzzy controller for an inverted pendulum.

This article presents an approach to embedding expert systems within an object oriented simulation environment. The basic idea is to create classes of expert system models that can be interfaced with other model classes. An expert system shell is developed within a knowledge-based design and simulation environment which combines artificial intelligence and systems modeling concepts. In the given framework, interruptible and distributed expert systems can be defined as components of simulations models. This facilitates simulation modeling of knowledge-based controls for flexible manufacturing and many other autonomous intelligent systems. Moreover, the structure of a system can be specified using a recursive system entity structure (SES) and unfolded to generate a family of hierarchical structures using an extension of SES pruning called recursive pruning. This recursive generation of hierarchical structures is especially appropriate for design of multilevel flexible factories. The article illustrates the utility of the proposed framework within the flexible manufacturing context.

An implementation of real-time simulation and control in DEVS-Scheme, a knowledge-based, discrete-event environment, is described. A methodology is illustrated in which the plant and its actuators and sensors are described by discrete-event models developed within the event-based control paradigm. A model of the controller is employed to validate its design in a plant/actuator/sensor experimental frame.>

A high autonomy system needs many models on which to base control, management, design, and other interventions. These models differ in level of abstraction and in formalism. Concepts and tools are needed to organize the models into a coherent whole. The abstraction processes for systematic derivation of related models for use in event-based control are discussed here. The multifaceted modeling methodology is briefly reviewed. The morphism concepts needed for application to model abstraction are described. A theory for supporting the construction of discrete event system specification (DEVS) models needed for event-based control is presented. A morphism implemented on the basis of this theory is also described.>

An extension of the discrete event system specification modeling formalism (DEVS) that facilitates symbolic expression of event times by extending the time base from the real numbers to the field of linear polynomials over the reals is presented. A simulation algorithm is developed to generate the branching trajectories resulting from the underlying nondeterminism. To efficiently manage symbolic constraints, a consistency checking algorithm for linear polynomial constraints based on a feasibility checking algorithm borrowed from linear programming is developed. The extended formalism offers a convenient means to conduct multiple, simultaneous explorations of model behaviors. Examples of application are given with concentration on fault model analysis.>

We discuss some of the key concepts and goals in the areas connected with qualitative and common-sense reasoning from the systems and simulation perspective. We critically examine the general research agenda associated with common-sense reasoning about physical systems and find much overlap with existing systems concepts. We suggest that a rapprochement with research in systems modelling could contribute to the progress of both fields. Indeed, both are concerned with enhancing systems problem solving—with the computer in a subsidiary role (systems research) or taking the lead (qualitative reasoning). We discuss some of the apparent misconceptions among artificial intelligence researchers about systems research and offer some suggestions for fruitful collaborations and research directions.

System entity structure (SES) is a structural knowledge representation scheme that contains knowledge of decomposition, taxonomy, and coupling of a system. Formally, the SES is a labeled tree with attached variable types that satisfy certain axioms. Described is a realization of the SES in Scheme (a Lisp dialect), that is called ESP-Scheme. Specifically, the computer representation of SES and main operations on SES are presented, and then facilities provided by ESP-Scheme are described. Two examples of application are discussed: a parallel processor model and a simulation study of a university phone registration system. ESP-Scheme acts as a model base management system in DEVS-Scheme, a knowledge-based simulation environment. It supports specification of the structure of a family of models, pruning the structure to a reduced version, and transforming the latter to a simulation model by synthesizing component models in the model base.>

This paper describes design and implementation of the hierarchical scheduling subsystem and graphical user interface in an intelligent environmental control system. The hierarchical scheduling system is capble of managing all environmental events occuring in widely different time scales as specified by the user. We employ a knowledge representation scheme called system entity structure to specify the environmental schedules in a hierarchical fashion. A system entity structure called TAL (Timed Action Language) is developed. TAL organizes a family of all possible long-/mid-/short-term schedules from which a specific schedule can be pruned by the user through graphical interface.

It is shown how systems can be advantageously represented as discrete event models by using DEVS (discrete event system specification), set-theoretic formalism. Such DEVS models provide a basis for the design of event-based logic control. In this control paradigm, the controller expects to receive confirming sensor responses to its control commands within definite time windows determined by its DEVS model of the system under control. The event-based control paradigm is applied in advanced robotic and intelligent automation, showing how classical process control can be readily interfaced with rule-based symbolic reasoning systems.>

A methodology is being developed to map hierarchical, modular discrete event models onto distributed simulator architectures. Concept developed for the first step of the methodology concerning model representation are discussed. The DEVS (Discrete Event System Specification) is extended to facilitate modular, hierarchical model specification. Procedures for top-down model development are expressed with the extended formalism and illustrated with a computer system model design.>

An application of the system entity structure is illustrated: a frame-like knowledge representation scheme is used to design local area networks (LANs). An entity structure for a data-link-layer protocol that illustrates many possible applications is introduced. The main concepts of the design methodology are illustrated using this example entity structure, and the underlying simulation environment is briefly discussed. The methodology aims to facilitate evaluation of a wide family of design alternatives and component combinations.>

A simulation consists of a triple of automata (system to be simulated, model of this system, computer realizing the model).In a valid simulation these elements are connected by behavior and structure preserving morphisms.Informational and complexity considerations motivate the development of structure preserving morphisms which can preserve not only global, but also local dynamic structure.A formalism for automaton structure assignment and the relevant weak and strong structure preserving morphisms are introduced.It is shown that these preservation notions properly refine the usual automaton homomorphism concepts.Sufficient conditions are given under which preservation of the local state space structure (weak morphism) also forces the preservation of component interaction.The strong sense in which these conditions are necessary is also demonstrated.This provides a rationale for making valid inferences about the local structure of a system when that of a behaviorally valid model is known.

It is known that for every integer d there are transition functions not isomorphically realizable by any net having feedback indegree (the largest number of wires that any delay receives from other delays in its feedback loop) less than d. Here we show that, in contrast to the isomorphic case, every transition function can be homomorphically realized by nets of feedback indegree not exceeding 2. This is a least upper bound, since simple nets (i. e., those having feedback indegrees not exceeding 1) are shown not to be universal in this sense.