DEVS Models Research Articles

Real-time simulation of DEVS models in CD++

The CD++ toolkit was developed in order to implement the theoretical concepts specified by the DEVS formalism. The tool allows the execution of both DEVS and ell-DEVS models. In this work, we present the definition and implementation of a real-time simulator. In such simulations, events must be handled timely and time constraints can be stated and validated accordingly. The new simulation technique allows the interaction between the model and its surrounding environment. Additionally, a non-hierarchical simulation approach is presented and introduced to CD++ in order to reduce the communication overhead.

DEVS Models of Palletized Ground Stacking in Storeyed Grain Warehouse

Processed grain stored in storeyed warehouse is generally stacked on the ground without pallets. However, in order to improve the storing way, we developed a new stacking method, palletized ground stacking. Simulation should be used to present this new storing way. DEVS provides a formalized way to describe the system model. In this paper, DEVS models of palletized ground stacking in storeyed grain warehouse are given and a simulation model is developed by AutoMod.

System Reliability using Simulation Models and Formal Methods

The general scope of the paper consists of improving the verification of simulation models through the integration of formal methods. We offer a formal verification approach of DEVS models based on Z notation. DEVS is a formalism that allows the description and analysis of the behavior of discrete event systems, i.e., systems whose state change depends on the occurrence of an event. A DEVS model is essentially validated by the simulation which permits of verifying whether it correctly describes the behavior of the system. However, a simulation does not cover all possible cases that means the model is validated only for the expected behaviors. For this reason, we have integrated the Z formal specification language in the DEVS formalism to detect errors before simulation which is still an important step for the validation. This integration consists of: (1) transforming a DEVS model into an equivalent Z specification and (2) verifying the consistency of the DEVS model on the resulting specification using the tools developed by the Z community. Such consistency is fulfilled by determinism and completeness. Thus, a DEVS model is subjected to an automatic formal verification before proceeding to its simulation.

CML-DEVS: A specification language for DEVS conceptual models

DEVS models are widely used in the research community, in the industry and even in military or defense departments. Therefore, several software tools exist for modeling and simulating these models. However, each of these tools has its specific input language and a DEVS model described within a particular framework cannot be simulated by a different one. Moreover, the practitioners willing to use one of these tools must have non-trivial programming skills or must ask to a programmer to translate their models into the language of the desired tool. In this paper, we present CML-DEVS, a language that allows the conceptual, abstract or mathematical representation of DEVS models, in terms of mathematical and logical expressions without involving programming issues. Models described with CML-DEVS can be automatically translated (i.e. compiled) into the input language of different modeling and simulation tools. We also present a set of rules to translate CML-DEVS models into models that can be simulated with well-known DEVS frameworks such as DEVS-Suite and PowerDEVS. These rules allow the implementation of a multi-target compiler.

Distributed simulation of DEVS and Cell-DEVS models using the RISE middleware

With the expansion of the Web, the desire toward global cooperation in the distributed simulation technology has also been on the rise. However, since current distributed simulation interoperability methods are coupled with system implementations, they place constraints on enhancing interoperability and synchronization algorithms. To enhance simulation interoperability on the Web, we implemented the RISE (RESTful Interoperability Simulation Environment) middleware, the first existing simulation middleware to be based on RESTful Web-services (WS). RISE is a general middleware that serves as a container to hold different simulation environments without being specific to a certain environment. RISE can hold heterogeneous simulations, and it exposes them as services via the Web. One of such services is called Distributed CD++ (DCD++) simulation system, an extension of the CD++ core engine that allows executing DEVS and Cell-DEVS models. Here, we introduce a proof-of-concept design and implementation of DCD++ using the distributed simulation using the RISE environment. We show how the RESTful WS interoperability style in RISE has improved the design, implementation and the performance of the DCD++ simulator. We also discuss a substantial performance improvement of the implementation of the RISE-based DCD++ presented here, showing many advantages of the RESTful WS presented here: improved interoperability, a seamless method to be connected into a cloud computing environment, and performance improvement when compared to our SOAP-based DCD++ in a similar testing environment.

Using a Discrete-Event System Specifications (DEVS) for designing a Modelica compiler

We introduce a new architecture for the design of a tool for modeling and simulation of continuous and hybrid systems. The environment includes a compiler based on Modelica, a modular and a causal standard specification language for physical systems modeling (the tool supports models composed using certain component classes defined in the Modelica Standard Library, and the instantiation, parameterization and connection of these MSL components are described using a subset of Modelica). Models are defined in Modelica and are translated into DEVS models. DEVS theory (originally defined for modeling and simulation of discrete event systems) was extended in order to permit defining these of models. The different steps in the compiling process are show, including how to model these dynamic systems under the discrete event abstraction, including examples of model simulation with their execution results.

Activity in PythonPDEVS

We introduce an activity-enhanced version of PythonPDEVS, a Parallel DEVS simulator. PythonPDEVS supports both sequential and distributed simulation. Both se- quential and distributed variants of PythonPDEVS exploit information about computa- tional activity to reduce simulation time. DEVS models can be augmented by the user with domain-specific information about computational load. This information is used by the simulator to improve performance.

Using Activity Metrics for DEVS Simulation Profiling

Activity metrics can be used to profile DEVS models before and during the simulation. It is critical to get good activity metrics of models before and during their simulation. Having a means to compute a-priori activity of components (analytic activity) may be worth when simulating a model (or parts of it) for the first time. After, during the simulation, analytic activity can be corrected using dynamic one. In this paper, we introduce McCabe cyclomatic complexity metric (MCA) to compute analytic activity. Both static and simulation activity metrics have been implemented through a plug-in of the DEVSimPy (DEVS Simulator in Python language) environment and applied to DEVS models.

Hybrid system modeling using the SIMANLib and ARENALib Modelica libraries

The ARENALib and SIMANLib Modelica libraries replicate the basic functionality of the Arena simulation environment and the SIMAN language. These libraries facilitate describing discrete-event models using the Arena modeling methodology. ARENALib and SIMANLib models can be combined with other Modelica models in order to describe complex hybrid systems (i.e., combined continuous-time and discrete-event systems). The implementation and design of SIMANLib and ARENALib is discussed. The ARENALib components have been built in a modular fashion using SIMANLib. The SIMANLib components have been described as Parallel DEVS models and implemented using DEVSLib, a Modelica library previously developed by the authors to support the Parallel DEVS formalism. The use of Parallel DEVS as underlying mathematical formalism has facilitated the development and maintenance of SIMANLib. The modeling of two hybrid systems is discussed to illustrate the features and use of SIMANLib and ARENALib: firstly, a soaking-pit furnace; secondly, the malaria spread and an emergency hospital. DEVSLib, SIMANLib and ARENALib can be freely downloaded from http://www.euclides.dia.uned.es/.

Formal verification and validation with DEVS-Suite: OSPF Case study

Validation is a degree of which how correct a model represents the behavior of its system counterpart from the perspective of intended use of the model. The degree of representation of the model or abstraction is determined by the modeler according to user demands and objectives. Whenever the modeler and simulation user’s demands are satisfied, the model is considered as valid.In this paper, verification and validation of the DEVS models in DEVS-Suite environment are discussed. A case example called OSPF–DEVS simulator is applied and verification and validation tests are performed on it to show usefulness of DEVS formalism. Performed verification and validation tests are followed using a technique developed by Forrester and Senge. Particular attention is paid to reliability and maintainability in view of the state-of-the-art network simulator ns-2. Results are documented to lend confidence to simulation users and to show DEVS-Suite environment’s capabilities not to increase model infrastructure.

클라우드 컴퓨팅 공동 환경의 네스티드 세션관리에서의 응용 및 오류 훅킹

본 논문은 규칙-기반 DEVS 모델링과 시뮬레이션 기법을 사용하면서 클라우드 컴퓨팅 공동 환경의 네스티드 세션 관리에서의 오류 감지 시스템의 성능 분석을 설명한다. 본 논문은 FDA(Fault Detection Agent)의 설계와 구축을 설명한다. FDA는 클라우드 컴퓨팅 공동 환경의 네스티드 세션 관리에서 멀티미디어 원격 제어를 위한 소프트웨어 오류를 감지하기에 적합한 에이전트이다. This paper explains a performance analysis of an error detection system running on nested session management of cloud computing collaboration environment using rule-based DEVS modeling and simulation techniques. In DEVS, a system has a time base, inputs, states, outputs, and functions. This paper explains the design and implementation of the FDA(Fault Detection Agent). FDA is a system that is suitable for detecting software error for multimedia remote control based on nested session management of cloud computing collaboration environment.

Dynamic Distributed Simulation of DEVS Models on the OSGi Service

Dynamic Distributed Simulation of DEVS Models on the OSGi Service

A new cell space DEVS specification: Reviewing the parallel DEVS formalism seeking fast cell space simulations

This paper introduces a new specification for cellular DEVS models that assures high performance. It starts with the parallel DEVS specification and derives a high performance cellular DEVS layer using the property of closure under coupling. This is done through converting the parallel DEVS into its equivalent non-modular form which involves computational and communication overhead tradeoffs. The new specification layer, in contrast to multi-component DEVS, is identical to the modular parallel DEVS in the sense of state trajectories which are updated according to the modular message passing methodology. The equivalency of the two forms is verified using simulation methods. Once the equivalency has been ensured, analysis of the models becomes a decisive factor in employing modularity in cellular DEVS models. Non-modular models guarantee the efficiency of the models in contrast to the current cellular DEVS implementation approaches. This was achieved by converting the cell space partially or fully into atomic model in order to eliminate inter-cell messages. However, the new specification needs an automated way to implement and verify models since they might become complicated ones.

Simulating adaptive service-oriented software systems

Simulation of dynamic service-based software systems is important for studying services that may change their composition and thus interactions at run-time. An approach based on Service Oriented Architecture-compliant DEVS (SOAD) and Dynamic Structure DEVS (DSDEVS) modeling approaches is developed to support structural changes in service model composition. To achieve this goal, a broker–executive model is devised based on the broker model defined for SOAD and the executive model defined for DSDEVS. The capability to simulate dynamic services is incorporated to the DEVS-Suite simulator. To demonstrate modeling of dynamic service-based software systems, a real voice communication system and a model of this system have been developed. The importance of enabling simulation-based design for adaptable systems is briefly discussed.

Mediator approach to direct workflow simulation

This paper presents a direct workflow simulation method with which the future enactment service processes of a BPM system can be simulated directly (i.e., without a model conversion). The proposed method may easily be implemented on a commercial BPM system by plugging in a couple of software modules (no internal modification of the BPM system is required). Previous researches on workflow simulation relied mostly on conversion methods in which process definition models (PDMs) are converted to simulation models and the simulation is performed by a separate simulator. More recently, a direct workflow simulation method based on the concept of listener was proposed. However, with the listener approach, (1) some internal modification of the BPM system is required, (2) PDMs have to be modified slightly, and (3) reliable simulation is not guaranteed. The direct workflow simulation approach proposed in this paper, which we call the mediator approach, is free of these shortcomings. Moreover, the mediator approach is suitable for workflow simulation involving multiple BPM systems. In a ‘direct’ workflow simulation, (1) the work-list handler of each participant is replaced by a participant simulator, (2) simulation is carried out by the workflow engine of the BPM system, and (3) a software module called synchronization manager (mediator or listener) handles time synchronization during simulation. In this paper, the architecture and detailed logic of the mediator are described as DEVS models. The behaviors of participant simulators are also described as DEVS models. The proposed workflow simulation method has been implemented on a commercial BPM system as well as on an academic BPM system, and an illustrative workflow simulation example is provided.

Performance Measurement of Dynamic Structure DEVS for Large-Scale Cellular Space Models

Dynamic structure Discrete Event System Specification (DSDEVS) is an advanced modeling formalism that allows DEVS models and their couplings to be dynamically changed. The modeling power and advantages of DSDEVS have been well studied, however, the performance aspect is generally overlooked. This paper provides a comprehensive performance measurement of DSDEVS for a large-scale cellular space model. We consider the modeling and simulation layers for performance analysis, and carry out performance measurement based on a token ring model and a fire spread model. The results show that DS modeling can improve simulation performance for large-scale cellular space models, due to the fact that it makes the simulation focus only on those active models, and thus is more efficient than when the entire cellular space is loaded. On the other hand, the DS overhead cannot be ignored and can become significant and even dominant when a large number of cells are dynamically added/deleted.

PARALLEL ALGORITHMS FOR CELLULAR MODELS SIMULATION

DEVS is a sound formal modeling and simulation (M&S) framework based on generic dynamic system concepts. Cell-DEVS is a formalism for cell-shaped models based on DEVS. This work presents a new simulation technique for execution of DEVS and Cell-DEVS models in parallel environments. These techniques are modifications to the original Time Warp mechanism offered by WARPED kernel. Time Warp functionalities are revised to include two new algorithms namely, Local Rollback Frequency Model (LRFM) and Global Rollback Frequency Model (GRFM). The resulting simulator is used as new simulation engine for CD++, an M&S toolkit that implements DEVS and Cell-DEVS theories. The results obtained allowed us to achieve considerable speedups due to the reductions that LRFM and GRFM protocols perform on number of rollbacks and anti-messages.

DEVS modeling of mobile wireless ad hoc networks

Ad hoc networks are self-organizing wireless systems conformed by cooperating neighboring nodes that conform networks with variable topology. Analyzing these networks is a complex task due to their dynamic and irregular nature. Cellular Automata (CA), a very popular technique to study self-organizing systems, can be used to model and simulate ad hoc networks, as the modeling technique resembles the system being modeled. Cell-DEVS was proposed as an extension to CA in which each cell in the system is considered as a DEVS model. The approach permits defining models with asynchronous behavior, and to execute them with high efficiency. We show how these techniques can be used to model mobile wireless ad hoc networks, making easy model definition, analysis and visualization of the results. The use of Cell-DEVS permitted us to easily develop new experiments, which allowed us to extend routing techniques for inter-networking and multicast routing, while permitting seamless integration with traditional networking models.

Formal DEVS modelling and simulation of a flow-shop relocation method without interrupting the production

This paper presents an organizational method of transfer of a flow-shop to a new site without interrupting the production. This method, which can be used even in case of requirements during the removal period, consists in segmenting the flow-shop removal into successive removals of groups of machines. This method can be successfully applied provided a prime condition is met: there must be sufficient stock upstream of the different groups of machines. The role of these stocks is to ensure continuity of production operations between the old and the new site, while a non-operational group of machines is being removed. The removal of groups of machines goes on until the whole production line is transferred to the new site and operational on this site. To validate this approach, we used a simulation and developed a flow-shop model according to the DEVS formalism. Our model makes it possible to segment a production line. We can therefore simulate a sequential transfer of groups of machines to the new site. The most effective solutions among those proposed suggest starting with the final group of machines (finished products) to finish with the first group. In this paper, we present and discuss some simulation results for an industrial case study. These results demonstrate the compared effectiveness of different removal strategies, and help decide for the appropriate estimated project management.

ATLAS: A language to specify traffic models using Cell-DEVS

The ATLAS specification language is devoted to build models of city sections using microsimulation. The basic language constructions allow defining a static topology of the section to be studied. The dynamic behavior of the section can be modified by including traffic lights, traffic signs, etc. Once the urban section is outlined, models are converted into cell spaces and the traffic flow is automatically set up. Language constructions were mapped into DEVS and Cell-DEVS models that can be easily executed with a simulation tool. The models were formally specified, improving the verification of the language. Thanks to this formal approach, we ensure that the simulations are correct, avoiding a high number of errors in the developed application, and as the modelers can focus in the problem to solve, development times can be reduced.