Herbert Praehofer

SYSTEM THEORETIC FORMALISMS FOR COMBINED DISCRETE-CONTINUOUS SYSTEM SIMULATION

In this paper we present an approach to combined discrete-continuous modelling which can be used to model and simulate an intelligent multi-layer control architecture as can be found in high autonomy systems. The modelling approach is based on system theoretical concepts; the three system specification formalisms-differential equation, discrete time, and the discrete event system specification formalism-have been combined to facilitate multi-formalisms modelling. Simulation concepts are based on the abstract simulator concept for discrete event simulation developed by Zeigler. Similar simulation methods have been developed to simulate modular, hierarchical discrete time and differential equation specified systems as well as multi-formalism models. Included in the paper are several examples of multi-formalism models together with the simulation results from the STIMS environment-an implementation of the modelling and simulation concepts in Interlisp-D/LOOPS.

DEVS Framework for Modelling, Simulation, Analysis, and Design of Hybrid Systems

We make the case that Discrete Event System Specification (DEVS) is a universal formalism for discrete event dynamical systems (DEDS). DEVS offers an expressive framework for modelling, design, analysis and simulation of autonomous and hybrid systems. We review some known features of DEVS and its extensions. We then focus on the use of DEVS to formulate and synthesize supervisory level controllers.

Visual modeling of DEVS-based multiformalism systems based on higraphs

This paper presents a graphical modeling method and tool for DEVS model and DEVS-based combined discrete/continuous model specification. In DEVS-based modeling, atomic model behavior specification is organized around different phases which define a partition of the state space of the model. The phase transitions depict the qualitative state changes and naturally lend themselves to be represented by a state transition diagram. Our representation of these phase transitions is based on the higraph extension to conventional graph representations. In higraphs, the area of the diagram is used to represent set enclosure and exclusion and the Cartesian product which leads to remarkable reduction in the diagrams complexity. An interactive modeling tool based on the graphical representation developed is presented.

Concepts and architecture of a simulation framework based on the JavaBeans component model

Abstract We report on a combination of system theoretic simulation modeling methodology with the JavaBeans component model as a basis for a component-based simulation framework. While system theory formalisms can serve as formal, mathematical foundations for modular, hierarchical modeling and simulation, the JavaBeans component model provides the appropriate implementation base. The result of the synergism is a powerful component-based simulation framework. In this paper we present the basic concepts and overall architecture of our JavaBeans modeling and simulation framework. We review the underlying system modeling formalisms for simulation modeling, sketch the layered architecture of the framework, and show elementary simulation programming and interface-based, hierarchical coupling of simulation components in more detail. Finally, we show the current state of implementation and demonstrate how simulation models can be developed using standard bean builder tools.

THEORY OF QUANTIZED SYSTEMS: DEVS SIMULATION OF PERCEIVING AGENTS

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.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.

An environment for DEVS-based multiformalism simulation in Common Lisp/CLOS

The paper presents the realization of an object-oriented kernel of a new modeling and simulation environment. The kernel system stands out as it is based on systems theoretical concepts and facilitates combined discrete-continuous, modular, hierarchical modeling. Its implementation language is the AI language Common Lisp and its object-oriented superset CLOS. The kernel system serves as the basis for a knowledge-based modeling and simulation environment supporting interactive modeling and simulation and automatic model construction.

Case-based reasoning techniques to support reusability in a requirement engineering and system design tool

Abstract CASA (computer aided systems architecting) is a methodology and tool to support the design of complex technical systems. It combines approaches from systems and requirement engineering and AI. System design in CASA is requirement-driven, and works by a hierarchical stepwise top-down refinement of designs and a hierarchical decision-making process. One important task in CASA deals with the reusability of existing design artifacts and is supported by case-based reasoning techniques. Based on given structural specifications and formal requirements, a search procedure finds the best inexact match in a design base and computes an estimated degree of fulfillment for requirements. The approach employs efficient graph-matching and indexing schemes for case retrieval and structural similarities, and has adapted usual similarity measures to compute degree of fulfillment of requirements. It has been shown by different sample projects that the developed methods can be of great practical assistance to a designer.

DEVS formalism as a framework for advanced distributed simulation

Advanced distributed simulation (ADS) is an enabling concept to support the networked interaction of models and real-world elements resident at geographically dispersed sites planned for next-generation simulation environments such as the Joint Simulation System (JSIMS). In this paper, we review the DEVS (discrete event systems specification) formalism and indicate why it provides the right framework to address many of the difficult technical issues that must be solved to enable ADS to provide infrastructures for distributed simulation. Then we address two of these issues in detail. The first issue addressed is the use of filtering and predictive contracts to reduce the tremendous amounts of data and control messages that must be transmitted in simulations. The second part focuses on scheduling and synchronization mechanisms for the efficient parallel execution of such models.

A discrete event system model of business system-a systems theoretic foundation for information systems analysis. I

A variety of information systems methodologies for information systems analysis have been proposed. Though each methodology has its own effective concepts and tools, there still does not seem to exist a rigorous model of a business system. In this paper a general model of business systems is proposed. The model describes the whole mechanism of typical routine processing of business tasks with slips and business papers. Furthermore it can be used to examine the ability and limitation of popular tools. The model proposed is called a business transaction system. It consists of both static and dynamic structures. The former depicts the interconnection of the transactions and file system in a business system. The dynamic structure is constructed as a state space representation by introducing a state space, and then the resultant dynamic system is a discrete event system. The state space consists of the file system and schedule of transactions processing. The model provides answers to some questions about the nature of information systems methodologies.

Distributed simulation of DEVS-based multiformalism models

In this paper we introduce a new approach for parallel, distributed simulation of modular, hierarchical DEVS and DEVS-based combined discrete/continuous multiformalism models. The algorithm combines conservative and optimistic distributed simulation strategies and is able to optimally exploit lookahead capabilities of the model. The object oriented implementation in C++ is intended to serve as a powerful simulator in the STIMS modeling and simulation environment.<<ETX>>