On the Need for Contextualized Introspective Models to Improve Reuse and Composability of Defense Simulations

dependency conditions are of interest? How can these dependencies be instrumental in capturing contextual dependencies of models? • What is the best way to package and distribute original context information along with simulation models to facilitate retrieval, understanding, and reasoning about the suitability of a simulation model in a new context? The rest of the paper is organized as follows. In Section 2 the role and significance of separating concept, content, context, and simulator are discussed. In Section 3 we overview related work on the development of contextaware computational artifacts. Section 4 discusses the elements of context and their interdependencies within a simulation modeling framework. The discreteevent system specification (DEVS) formalism is used as a basis to outline elements of context and their interdependencies. The notion of abstract behavioral component relationships is used to structure the contextual dependencies of a simulation model. In Section 5 a novel model design strategy that facilitates storage and retrieval of structured context information is suggested. We conclude (Section 6) by discussing the utility and limitations of the strategy, as well as potential avenues for further research. 2. The Separation of Concept, Content, Context, and Simulator A model is a representation of the system, entity, phenomenon, or process. Simulation is the act of using a simulator (simulation engine or a behavior generator) to drive simulation models to generate model behavior. A conceptual model is an abstract model that incorporates a specification (i.e., DEVS I/O system specification [22] that represents some aspects of reality that is delimited with reference to the goal of the study. A simulation model, on the other hand, is the computerized version of an abstract conceptual model. More specifically, a model associated with a simulation study is expressed within a computer program and this computer code embodiment of a model is called a simulation model. Experimental frame refers to the specification of the conditions under which the model is observed or experimented with. Figure 1 depicts these components as well as their interdependencies. While modularity has been widely acknowledged as an enabling factor for composability in software intensive system development [24], little attention is devoted to the role and significance of the separation of concerns with respect to these fundamental M&S framework components. 2.1 The Separation of Concept from Content The separation, explicit representation, and reference to the concept (specification) components within a simulation model not only enable qualification of a model for reuse on the basis of its formal specification, but also facilitate substitutability of alternative simulation models that implement the same concept. While none of the existing simulation modeling environments provides language facilities to relate a simulation model to its specification, availability of such a formal specification (i.e., DEVS I/O system specification) in some form that is independent of the simulation model enables substitutability analysis between the context of the new experiment and the potentially reusable model component. Distributing specification of a simulation model as part of the simulation software using embedded comments may not be practical since it requires discovery, location, and interpretation of such comments. Hence, explicit reference to a specification component within a simulation model representation would simplify the selection of a model for assembly during composition.