1. Unifying Discrete and Continuous Simulation with Discrete Events: DEVS as the Next Modeling Standard Bernard P. Zeigler Arizona Center for Integrative Modeling and Simulation University of Arizona Tucson www.acims.arizona.edu

2. Outline Why is a formal framework for M&S needed? –for independent V&V –for simulation component reuse –for standardization at the right level Systems-based framework for M&S –Discrete Event System Specification (DEVS) –Representing Continuous Systems in DEVS –Speed up advantages

3. Simulation-based V&V as an afterthought development of the system simulation tests of the system Government Contractor

4. Government’s Desire for Independent Simulation- based V&V of new Systems simulation environment / test plans/events for V&V Another Contractor specification of the system development of the system Government Contractor simulation tests of the system

5. How is simulation software different from other software? It represents the behavior of dynamic systems whose states are functionally dependent on time Properly controlling the flow of time is critical Simulation software may combine: –continuous (time-driven) and discrete (event-driven) processes –actual operating hardware and software representations –wall clock and {faster/slower} than real time advance

6. independent specification of the desired deliverable – how the dynamic system behaves over time methods needed to compare the behaviors of the system representation and the independent specification A Formal Framework for Modeling and Simulation should provide DEVS Experimental Frames

7. DEVS = Discrete Event System Specification Provides formal M&S framework: specification,simulation Derived from Mathematical dynamical system theory Supports hierarchical, modular composition Object oriented implementation Supports discrete and continuous paradigms Exploits efficient parallel and distributed simulation techniques DEVS Background

8. DEVS Hierarchical Modular Model Framework Atomic: lowest level model, contains structural dynamics -- model level modularity + coupling Coupled: composed of one or more atomic and/or coupled models hierarchical construction

9. DEVS Examples Lockheed Martin’s Managed M&S Univ. New Mexico’s Virtual Lab

10. Managed Modeling in Lockheed’s “System of Systems” M&S Environment DEVS (Discrete Event Modeling Formalism) –Separates Model and Simulators –Defines Couple Models and Atomic Models –Modularized via Ports and Defined Events SES (System Entity Structure) –Provides a well defined structure for model reuse –Maintains: kind-of, part-of, multiplicity relationships –Supports constraints on model compatibility Architecture based on SES/DEVS supports component model reuse during last decade

11. Component Model Reuse Matrix Project Model Critical Mobile Target Global Positioning System III Arsena l Ship Coast Guard Deep Water Space Operation s Vehicle Common Aero Vehicle Joint Composit e Tracking Network Integrate d System Center Space Based Laser Space Based Discrimin ation Missile Defense (Theater / National) Radar Model xxxxxxx IR Sensor Model xxxxxxx Missile Model xxxxx Laser Model xxxx Comm. Model xxxxxx Comman d Control Model xxx Earth & Terrain Model xxxxx Weather Model xx Waypoint & Heading Nav Model xxxxxxx Orbital Propagat e Model xxxxxxx Ballistic Trajector y Model xxxxx

12. University of New Mexico Virtual Lab for Autonomous Agents V-Lab-a virtual laboratory for autonomous agents-SLA-based learning controllers El-Osery, A.I.; Burge, J.; Jamshidi, M.; Saba, A.; Fathi, M.; Akbarzadeh-T, M.-R.; Systems, Man and Cybernetics, Part B, IEEE Transactions on, Volume: 32 Issue: 6, Dec. 2002 Page(s): 791 -803 Physics Terrain Dynamic SimEnv ControlAgentsSimMan Computer Network Middleware (HLA,CORBA,JMS) DEVS Simulator IDEVSSimEnv V-Lab developed on top of DEVSJAVA includes a simulation environment for robotic agents with physics, terrain and dynamics. It extends DEVS to provide a layer for specifying intelligent automation and soft computing algorithms (IDEVS).

13. "Priorities for M&S Standards” Monday, 31 March 03 Standardization should be aimed at the modeling/specification level… "Priorities for M&S Standards” Monday, 31 March 03

14. Partial

15. Mapping Differential Equation Models into DEVS Integrator Models DEVS instantaneous function DEVS Integrator  d s 1 /dt s 1 f 1 x  d s 2 /dt s 2 f 2  d s n /dt s n f n s x s x s x...  d s 1 /dt s 1 f 1 x  d s 2 /dt s 2 f 2  d s n /dt s n f n s x s x s x... DEVS S F F F

16. Number of crossings = Activity/quantum Activity – a characteristic of continuous models Activity = |f(t1) – f(t0)|

17. DEVS Efficiency Advantage where Activity is Heterogeneous in Time and Space Time Period T time step size # time steps =T/ activity A quantum q # crossings =A/q Potential Speed Up = #time stops / # crossings X number of cells

18. 1 D Gas Dynamics Example Heterogeneous activity in time and space More: http://www.ece.arizona.edu/~salila/movies

19. Activity as unifying continuous and discrete paradigms Heterogeneous activity in time and space Quantization allows DEVS to naturally focus computing resources on high activity regions DEVS represents all decision making and continuous dynamic components in the scene

20. Summary The theory of modeling and simulation has provides a framework to represent classes of continuous and discrete systems and to develop object-oriented simulation frameworks to interoperate such models. There is an urgent need to come up with new principles to unify discrete and continuous modeling paradigms, to encode them into modeling standards and to develop simulation standards for effectively and efficiently executing these models. This talk presented a basis for discrete event abstractions by formalizing the concept of activity which relates to the characterization and heterogeneous distribution of events in space and time. This formulation offers a new way to unify the computational representation of both continuous and discrete phenomena and simulate them with the greater efficiency and flexibility afforded by object-oriented discrete event environments.. On this basis, the DEVS (Discrete Event System Specification) formalism is the right vehicle for standardization at the modeling and simulation levels, augmenting existing interoperability standards such as HLA.