The limitations of model-based support for engineering complex systems include limited capability to develop multifaceted models as well as their analysis with robust reliable simulation engines. Lack of such Modeling and Simulation (M&S) infrastructure leads to knowledge gaps in engineering such complex systems and these gaps appear as epistemological emergent behaviors. In response, an initiative is underway to bring Model-Based Systems Engineering (MBSE) closer together with model-based simulation developments. M&S represents a core capability and is needed to address today’s complex, adaptive, systems of systems engineering challenges. This paper considers the problems raised by MBSE taken as a modeling activity without the support of full strength integrated simulation capability and the potential for, and possible forms of, closer integration between the two streams. An example of a system engineering application, an unmanned vehicle fleet providing emergency ambulance service, is examined as an application of the kind of multifaceted M&S methodology required to effectively deal with such systems.

Discrete Event Specification (DEVS) environments are implemented over middleware systems such as HLA, RMI, CORBA and others. DEVS exhibits concepts of systems theory and modeling and supports capturing the system behavior from the physical and behavioral perspectives. Further, they are implemented using object-oriented languages like Java and C++. This research work uses the Java platform to implement DEVS over a Service Oriented Architecture (SOA) framework. Called the DEVS/SOA, the framework supports a development and testing environment known as DEVS Unified Process that is built on a model continuity-based lifecycle methodology. DEVS Unified Process allows DEVS-based Modeling and Simulation (M&S) over net-centric platforms using DEVS/SOA. This framework also provides the crucial feature of run-time composability of coupled systems using SOA. We describe the architecture and designs of the server and the client. The client application communicates with multiple servers hosting DEVS simulation services. These simulation services are developed using the proposed symmetrical services architecture wherein the server can act as both a service provider and a service consumer contrary to the unidirectional client—server paradigm. We also discuss how this services-based architecture provides solutions for cross-platform distributed M&S. We demonstrate the DEVS/SOA framework with a scenario of Joint Close Air Support specified in Business Process Modeling Notation (BPMN). We also provide a real-world application of network health monitoring using DEVS/SOA-layered architectural framework.

Variable structure refers to the ability of a system to dynamically change its structure according to different situations. It provides component-based modeling and simulation environments with powerful modeling capability and the flexibility to design and analyze complex systems. In this article, the authors discuss variable structure—specifically, the structure change and interface change capability—in DEVS-based modeling and simulation environments. The operations of structure change and interface change are discussed, and their respective operation boundaries are defined. Three examples are given to illustrate the role of variable structure and how it can be used to model and design adaptive complex systems. Principles for the implementation of variable structure are also presented and illustrated in the DEVSJAVA modeling and simulation environment.

A recent DoD mandate requires that the DoD Architecture 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 systems views, which provide its technical attributes, forms the basis for semi-automated construction of the needed simulation models. Unfortunately, DoDAF doesn't mandate any simulation methodology to analyze the system or perform any pre-design feasibility studies. 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 life cycle development process that includes both development and testing in an integral manner. We introduce two new operational views (OVs) in the current DoDAF making way for modeling and simulation as a part of the design process. We illustrate the process to build these new OVs from the existing OVs and their impact on the overall DoDAF system development process. We discuss automated model generation using XML through the introduced OVs, which paves the way for OVs to become service-providing components in the web services architecture.

Modeling and simulation (M&S) for system design and prototyping is practiced today both in industry and academia. M&S are two different areas altogether and have specific objectives. However, most of the time these two separate areas are taken together. The developed code is woven tightly around both the model and the underlying simulator that executes it. This constrains both the model development and the simulation engine that has an impact on the scalability of the developed code. Furthermore, a lot of time is spent in developing a model because it needs both domain knowledge and simulation techniques, which also requires communication among users and developers. The Unified Modeling Language (UML) is widely accepted in industry, whereas discrete event specification (DEVS)-based modeling that separates the model and the simulator, provides a cleaner methodology to develop models and is much used in academia. DEVS today is used by engineers who understand discrete event modeling at a highly detailed level and are able to translate requirements to DEVS modeling code. There have been earlier efforts to integrate UML and DEVS but they have not succeeded in providing a transformation mechanism owing to inherent differences in these two modeling paradigms. In this paper we present an integrated approach to cross-transformations between UML and DEVS using the proposed eUDEVS, which stands for executable UML based on DEVS. Further, we also show that the obtained DEVS models belong to a specific class of DEVS models called finite deterministic DEVS (FD-DEVS) that is available as a W3C XML schema in XFD-DEVS. We also put the proposed eUDEVS in a much larger unifying framework called the DEVS unified process that allows bifurcated model-continuity-based lifecycle methodology for systems M&S. Finally, we demonstrate the concepts with a complete example.