System Specification Formalism Research Articles

Configuration space–based discrete event system specification formalism for a smart factory with real-time flexibility

A manufacturing system consists of various manufacturing devices, and each device has a set of tasks which are triggered by specific commands. Traditionally, simulation has been considered as an essential technology for the evaluation and analysis of manufacturing systems. Although discrete event system specification formalism has been a popular modeling tool for manufacturing systems, it has limitations in describing situations such as sudden cancelation of tasks. Proposed in this article is an extended discrete event system specification formalism for the effective description of a smart factory which requires the intelligence to handle turbulences in real-time production. The extended discrete event system specification formalism incorporates the configuration space concept, which is well-known in classical mechanics. While the conventional discrete event system specification formalism uses only the logical states set to represent the device states, the proposed formalism employs the combination of two sets: a logical states set (sequential states set) and a physical states set (configuration space of the device). As a result, the extended formalism enables the effective description of nondeterministic tasks which may occur frequently in a smart factory.

Zone-based formal specification and timing analysis of real-time self-adaptive systems

Self-adaptive software systems are able to autonomously adapt their behavior at run-time to react to internal dynamics and to uncertain and changing environment conditions. Formal specification and verification of self-adaptive systems are tasks generally very difficult to carry out, especially when involving time constraints. In this case, in fact, the system correctness depends also on the time associated with events.

Discrete Event System Specification Framework for Self-Improving Healthcare Service Systems

A healthcare service system (HSS) is made of humans and technology where for the foreseeable future, self-improvement will be primarily based on human understanding rather than machine learning. Therefore, for such a system to continually self-improve, it must provide the right data and models to support human decisions on selection of alternatives likely to improve the quality of its services. Our focus in this paper is to show how modeling and simulation (M&S) can help design service infrastructures that introduce coordination and bring into play the conditions for learning and continuous improvement. To do this, we discuss the application of the discrete event system specification (DEVS) formalism within system of systems engineering (SoSE) to develop coordination models for transactions that involve multiple disparate activities of component systems and that need to be selectively sequenced to implement patient-centered coordinated care interventions. We show how such coordination concepts provide a layer to support a proposed information technology for continuous improvement of healthcare as a learning collaborative system of systems (SoS).

Formal Specification and Verification of Self-Adaptive Concurrent Systems

The assurance of required quality properties is one of the major challenges in self-adaptive systems (SASs). SASs have the capability to adapt their dynamic behavior autonomously at runtime due to uncertain changes in the environment. In general, an SAS is much difficult to specify and verify, because of its highly complex internal behavior and especially when time constraints are involved. In this research, we use modal $\mu $ -calculus ( $\mathcal {M_{\mu }}$ ) for the specification and verification of colored Petri nets-based self-adaptive concurrent systems. We propose self-adaptive multi-agent concurrent system (SMACS) framework that is specifically designed for complex architectures. The internal structure of SMACS framework is based on MAPE-K feedback loop. Each phase of the feedback loop works as an internal agent (Int-Agent) known as Monitor Int-Agent, Analyzer Int-Agent, Planer Int-Agent, and Executer Int-Agent. The decentralized approach is being used in this research, and due to this approach, all agents intelligently adapt their behavior in the environment and send updates to other agents. For verification of internal properties like liveness, safeness, and deadlock-freedom of each agent, the TAPA model checker is being used. For the implementation of SMACS framework, traffic monitoring system is chosen as a case study.

RPDEVS: Revising the Parallel Discrete Event System Specification

In this work, we present a Revised Parallel DEVS (RPDEVS) formalism. The Classic Discrete Event System Specification (DEVS) and Parallel DEVS (PDEVS) formalisms do not support modelling of ‘true’ mealy behaviour, i.e. reacting to an input message immediately with an output message. Instead, such behaviour has to be modelled via transitory states and multiple state updates. This not only increases model complexity, it also impedes reusability of model components in different contexts.RPDEVS enhances PDEVS with the capability to model mealy behaviour directly. Hence, the output function λ can access the input bag. This introduces some challenges regarding the simulation algorithm which we will take a look at.Further, the terms algebraic loop and illegitimate model will be discussed in the context of RPDEVS. It is shown that RPDEVS models which are free of algebraic loops are also legitimate. Finally, it will be demonstrated that like Classic DEVS and PDEVS, also RPDEVS provides closure under coupling.

Development of stratified approach to software defined networks simulation

The stratified approach to software defined networks simulation has been proposed. It is based on Discrete Event System Specification formalism, atomic and coupled models concepts usage. The approach is aimed at simulation within the Windows environment, with an accent on the easiness of model reconfiguration. The proposed approach is also devoted to simulation-related overheads decrease. The atomic models of active (controller, switch, host) and passive (link) network components have been proposed. The coupled model of a software defined network comprising atomic models of active and passive components has been proposed. The estimations of the resulting coupled model complexity, with respect to the number of components basic atomic models, have been given. During experimentation, the pingall command usage scenario has been considered. For this purpose, the emulation via Mininet environment and the simulation on a basis of the proposed approach have been conducted. It has been shown that discrete-event simulation on a basis of the proposed approach is significantly less time-consuming. During the approach usage within the Windows environment, the absence of the need to utilize the Xming X Server and PuTTY utility for the purpose of visualization has been faced. The validity of the approach has been proven on a basis of the obtained experimental data. The adequacy of the resulting coupled simulation model of the network has been proven with t-criterion. The proposed approach can be used for the purpose of software defined networks validation with an accent on non-functional properties

Multiscale representation of simulated time

To better support multiscale modeling and simulation, we present a multiscale time representation consisting of data types, data structures, and algorithms that collectively support the recording of past events and scheduling of future events in a discrete event simulation. Our approach addresses the drawbacks of conventional time representations: limited range in the case of 32- or 64-bit fixed-point time values; problematic rounding errors in the case of floating-point numbers; and the lack of a universally acceptable precision level in the case of brute force approaches. The proposed representation provides both extensive range and fine resolution in the timing of events, yet it stores and manipulates the majority of event times as standard 64-bit numbers. When adopted for simulation purposes, the representation allows a domain expert to choose a precision level for his/her model. This time precision is honored by the simulator even when the model is integrated with other models of vastly different time scales. Making use of C++11 programming language features and the Discrete Event System Specification formalism, we implemented a simulator to test the time representation and inform a discussion on its implications for collaborative multiscale modeling efforts.

Improving Video Transmission in Cellular Networks with Cached and Segmented Video Download Algorithms

Satisfying the increasing demand for high data rates has become a main challenge for cellular network operators. Moreover, the demand for video traffic in cellular networks has been continuously increasing. In 2016, wireless video accounted for more than half of the total mobile data traffic, and it is expected to further increase in the upcoming years. This will increase the amount of data to be transmitted in cellular networks, and further increase the challenge for cellular network operators. Device-to-Device (D2D) communication, introduced by the Long Term Evolution-Advanced (LTE-A) standard, is a new communication technique that allows direct communication between devices in cellular networks without going through the Base-Station (BS). We present two algorithms for improving the throughput of video transmission in cellular networks. The algorithms are called Cached and Segmented Video Download (CSVD), and DIStributed, Cached, and Segmented video download (DISCS). The algorithms send segments of video files to selected User Equipments (UEs) in the cellular network, to cache and forward them to requesting UEs using D2D communication. We study the performance of both algorithms analytically in terms of the hit ratio. Furthermore, we use the Discrete EVent System Specification (DEVS) formalism to build an LTE-A network model and use the model to study the performance of CSVD and DISCS in terms of the cell’s aggregate data rate as well as the average data rate. Simulation results show that CSVD and DISCS achieve significant performance improvements in terms of the aggregate and average data rates.

A novel simulation method for power electronics: discrete state event driven method

In the analysis of power electronics system, it is necessary to simulate ordinary differential equations (ODEs) with discontinuities and stiffness. However, there are many difficulties in using traditional discrete-time algorithms to solve such equations. Kofman and others presented the quantized state systems (QSS) algorithm in the discrete event system specification (DEVS) formalism. The discretization is applied to the state variables instead of time range in QSS. QSS is efficient to solve ODEs, but it is difficulty to be used when simulating actual power electronics systems with controller’s and other events. Based on the idea of this numerical algorithm and discrete event, a Discrete State Event Driven (DSED) simulation method is presented in this paper, which is fit for simulation of power electronics system. The method is developed to deal with non-linearity, stiffness and multi-time scale of power electronics systems. The DSED simulation method includes event definition, module seperation and modeling, event-driven mechanisms, numerical computation based on QSS, and some other operations. Simulation results verified the effectiveness and validity of the proposed method.

Practical aspects of the DesignDEVS simulation environment

DesignDEVS is a simulation development environment based on the Discrete Event System Specification (DEVS) formalism. This paper provides an in-depth overview of the software while focusing on the practical considerations influencing its design. Practitioners who stand to benefit from systems engineering will approach formalism-based simulation tools with little knowledge of the underlying theory. It is therefore important that theoretical principles, such as the separation of model and simulator, be emphasized by the user interface. Other practical aspects of DesignDEVS include the simplicity of atomic model code, a focus on coupling for collaboration purposes, the enforcement of essential modeling constraints, and a reliance on best practices in cases where strict enforcement might inconvenience users. In DesignDEVS, an issue we refer to as the Insidious Pointer Problem is aggressively tackled through run-time error handling. By contrast, the separation of output values from state transitions is left as a best practice for the sake of user convenience. The design decisions explained in this paper are relevant to developers of other formalism-based tools seeking widespread adoption of scalable modeling and simulation practices.

Modular representation of asynchronous geometric integrators with support for dynamic topology

Geometric integrators play an essential role for simulating second-order energy preserving systems, offering an alternative to the decomposition of systems into first-order Ordinary Differential Equations. This approach, although commonly used nowadays in modeling and simulation software, is not acceptable when long simulation runs are required. In this work we develop a modular representation of geometric, adaptive step-size integrators using the Heterogeneous Flow Systems Specification (HyFlow) formalism. Modularity is achieved in HyFlow through the use of an explicit definition of sampling that is treated as a first-order construct, enabling a novel representation of continuous systems and their seamless integration. We show that the HyFlow representation enables the interoperability of geometrical integrators with other families of models including, for example, conventional integrators, enhancing the ability to represent complex systems. HyFlow sampling enables geometric integrators to operate asynchronously, contributing to simulation efficiency by allowing the sampling rate to de defined independently by each component. We demonstrate that HyFlow-based geometric integrators can be used to model systems with a dynamic topology. In addition, we show that the modifying model topology at run-time can provide an effective solution to some systems exhibiting Zeno behavior.

Using the Parallel DEVS Protocol for General Robust Simulation with Near Optimal Performance

The Discrete Event Systems Specification (DEVS) formalism has been widely disseminated in this magazine and elsewhere for its applicability to computational science and engineering. While research in parallel and distributed simulation has been active in the past several decades, the utility of many techniques for high-performance DEVS simulation has been limited. Recent research has shown that that a reconstruction of Amdahl's and Gustafson's laws for parallelizing sequential code can afford a better understanding of the underlying principles and their application to simulation of DEVS models. In this article, the author shows, in comparison to the ideal case, that a relatively simple protocol based on the DEVS abstract simulator is both generally applicable and able to achieve significant speedup in parallel distributed simulation.

Design and simulation of distributed IMA architectures using TTEthernet: a model-driven approach

Integrated modular avionics architectures complemented with time-triggered ethernet (TTEthernet) provides a strong platform to support the design and deployment of distributed avionic software systems. The complexity of the design and continuous integration of such systems can be managed using a model-based methodology. In this paper, we present an extension for the AADL modeling language to support modeling TTEthernet-based distributed systems. This extension consists essentially in a metamodel of the TTEthernet standard and the implementation of its corresponding concrete syntax. Furthermore, we leverage model transformations to enable undertaking the verification of the system models expressed using our AADL extension. In particular, we propose to transform the system model to a model suitable for a simulation using the discrete event system specification formalism. We illustrate the proposed approach using an example of a navigation and guidance system and we use this example to show the verification of the contention-freed property of TTEthernet schedule.

Mining parametric temporal logic properties in model-based design for cyber-physical systems

One of the advantages of adopting a Model Based Development (MBD) process is that it enables testing and verification at early stages of development. However, it is often desirable to not only verify/falsify certain formal system specifications, but also to automatically explore the properties that the system satisfies. In this work, we present a framework that enables property exploration for Cyber-Physical Systems. Namely, given a parametric specification with multiple parameters, our solution can automatically infer the ranges of parameters for which the property does not hold on the system. In this paper, we consider parametric specifications in Metric or Signal Temporal Logic (MTL or STL). Using robust semantics for MTL, the parameter mining problem can be converted into a Pareto optimization problem for which we can provide an approximate solution by utilizing stochastic optimization methods. We include algorithms for the exploration and visualization of multi-parametric specifications. The framework is demonstrated on an industrial size, high-fidelity engine model as well as examples from related literature.

Reconsidering the performance of DEVS modeling and simulation environments using the DEVStone benchmark

The discrete event system specification formalism, which supports hierarchical and modular model composition, has been widely used to understand, analyze and develop a variety of systems. Discrete event system specification has been implemented in various languages and platforms over the years. The DEVStone benchmark was conceived to generate a set of models with varied structure and behavior, and to automate the evaluation of the performance of discrete event system specification-based simulators. However, DEVStone is still in a preliminary phase and more model analysis is required. In this paper, we revisit DEVStone introducing new equations to compute the number of events triggered. We also introduce a new benchmark with a similar central processing unit and memory requirements to the most complex benchmark in DEVStone, but with an easier implementation and with it being more manageable analytically. Finally, we compare both the performance and memory footprint of five different discrete event system specification simulators in two different hardware platforms.

Temporal Modeling of Neural Net Input/Output Behaviors: The Case of XOR

In the context of the modeling and simulation of neural nets, we formulate definitions for the behavioral realization of memoryless functions. The definitions of realization are substantively different for deterministic and stochastic systems constructed of neuron-inspired components. In contrast to earlier generations of neural net models, third generation spiking neural nets exhibit important temporal and dynamic properties, and random neural nets provide alternative probabilistic approaches. Our definitions of realization are based on the Discrete Event System Specification (DEVS) formalism that fundamentally include temporal and probabilistic characteristics of neuron system inputs, state, and outputs. The realizations that we construct—in particular for the Exclusive Or (XOR) logic gate—provide insight into the temporal and probabilistic characteristics that real neural systems might display. Our results provide a solid system-theoretical foundation and simulation modeling framework for the high-performance computational support of such applications.

Performance analyses of naval ships based on engineering level of simulation at the initial design stage

Naval ships are assigned many and varied missions. Their performance is critical for mission success, and depends on the specifications of the components. This is why performance analyses of naval ships are required at the initial design stage. Since the design and construction of naval ships take a very long time and incurs a huge cost, Modeling and Simulation (M & S) is an effective method for performance analyses. Thus in this study, a simulation core is proposed to analyze the performance of naval ships considering their specifications. This simulation core can perform the engineering level of simulations, considering the mathematical models for naval ships, such as maneuvering equations and passive sonar equations. Also, the simulation models of the simulation core follow Discrete EVent system Specification (DEVS) and Discrete Time System Specification (DTSS) formalisms, so that simulations can progress over discrete events and discrete times. In addition, applying DEVS and DTSS formalisms makes the structure of simulation models flexible and reusable. To verify the applicability of this simulation core, such a simulation core was applied to simulations for the performance analyses of a submarine in an Anti-SUrface Warfare (ASUW) mission. These simulations were composed of two scenarios. The first scenario of submarine diving carried out maneuvering performance analysis by analyzing the pitch angle variation and depth variation of the submarine over time. The second scenario of submarine detection carried out detection performance analysis by analyzing how well the sonar of the submarine resolves adjacent targets. The results of these simulations ensure that the simulation core of this study could be applied to the performance analyses of naval ships considering their specifications.

Formal Specification and Verification of System of Systems Using UPPAAL: A Case Study of a Defensive Missile Systems

Formal Specification and Verification of System of Systems Using UPPAAL: A Case Study of a Defensive Missile Systems

SiMAMT

Multi-agent multi-team systems are commonly seen in environments where hierarchical layers of goals are at play. For example, theater-wide combat scenarios where multiple levels of command and control are required for proper execution of goals from the general to the foot soldier. Additionally, similar structures can be seen in game environments, where agents work together as teams to compete with other teams. The different agents within the same team must, while maintaining their own “personality”, work together and coordinate with each other to achieve a common team goal. This paper develops strategy-based multi-agent multi-team systems, where strategy is framed as an instrument at the team level to coordinate the multiple agents of a team in a cohesive way. The authors present SiMAMT, a framework for strategy-based multi-agent multi-team systems. The different components of the framework, including strategy simulation, strategy inference, strategy evaluation, and strategy selection are described. A formal specification of strategy and strategy-based multi-agent multi-team systems is provided. An example and experimental results are given to illustrate the proposed framework and its efficacy.

Formal Specification and Verification of System of Systems Using UPPAAL: A Case Study of a Defensive Missile Systems

Formal Specification and Verification of System of Systems Using UPPAAL: A Case Study of a Defensive Missile Systems