MS Thesis Presentation by Tarun Rathnam
Thursday, August 12, 2004

(Dr. C.J.J. Paredis, Chair)

"Using Ontologies to Support Interoperability in Federated Simulation"

Abstract

A vast array of computer-based simulation tools are used to support engineering design and analysis activities. Several such activities call for the simulation of various coupled sub-systems in parallel, typically to study the emergent behavior of large, complex systems. Most sub-systems have their own simulation models associated with them, which need to interoperate with each other in a federated fashion in order to simulate system-level behavior. The run-time exchange of information between federate simulations requires a common information model that defines the (representation of) entities (simulation objects and events) that simulators can publish or subscribe to. However, most federate simulations employ disparate representations of shared concepts. To address the problem of disparate representations, federate simulation developers must agree upon a common representation for concepts that are exchanged at runtime and modify their simulation models accordingly. Furthermore, it is often necessary, especially for legacy simulators, to implement transformation stubs that convert objects and events from the common representation to those used in the legacy implementation. The tasks of defining a common representation for shared simulation concepts, modifying individual simulations and building translation stubs around them can add significant time and cost to defining a system-level simulation.


In this thesis, a framework to support automation in the process of achieving interoperability between federate simulations is developed. This framework uses ontologies to capture knowledge about the semantics of different simulation concepts in a formal, reusable fashion. Using these semantics, a common representation for shared simulation entities, and a corresponding set of transformation stubs to convert entities from their federate to common representations (and vice-versa) are derived automatically. In capturing the description of simulation models and the relationships between them in a formal manner, this framework also supports the simplified re-use of federate simulations in multiple federations. As a foundation to this framework, a schema to enable the capture of simulation concepts in an ontology is specified. Further, steps are elaborated for capturing knowledge as to the relationship between different federate simulation entities. Finally, a graph-based algorithm is developed to extract the appropriate common information model and transformation procedures between federate and common simulation entities.


As a proof of concept, this framework is applied to support the development of a federated air traffic simulation. To progress with the design of an airport, the combined operation of its individual systems (air traffic control, ground traffic control, and ground-based aircraft services) in handling varying volumes of aircraft traffic is to be studied. To do so, the individual simulation models corresponding to the different sub-systems of the airport needs to be federated. The ontology-based framework is employed to support the development of this federation