Dependable systems are usually designed with multiple instances of components or logical processes, and often possess symmetries that may be exploited in model-based evaluation. The problem of how best to exploit symmetry in models has received much attention from the modeling community, but no solution has garnered widespread support, primarily because each solution is limited in terms of either the types of symmetry that can be exploited or the difficulty of translating from the system description to the model formalism. We propose a new method for detecting and exploiting model symmetry in which 1) models retain the structure of the system, and 2) all symmetry inherent in the structure of the model can be detected and exploited for the purposes of state-space reduction. Composed models are constructed from models through specification of connections between models that correspond to shared state fragments. The composed model is interpreted as an undirected graph, and results from group and graph theory are used to develop procedures for automatically detecting and exploiting all symmetries in the composed model. A statespace generator which implements these algorithms within Möbius [10] is then presented.12th Pacific Rim International Symposium on Dependable Computing (PRDC'06) 0-7695-2724
Despite the development of many modeling formalisms and model solution methods, most tool implementations support only a single formalism. Furthermore, models expressed in a chosen formalism cannot be combined with models expressed in other formalisms. This paper describes a modeling tool called Möbius, which provides an infrastructure to support multiple interacting formalisms and solvers, and is extensible in that new formalisms and solvers can be added to the tool such that they can interact with those already implemented without requiring additional changes to the previously implemented ones. We discuss the initial implementation of Möbius, and the recent addition of different formalisms and solution techniques to the tool.
The Möbius modeling environment is an extensible framework for discrete-event system analysis that allows multiple formalisms and solution techniques to easily interoperate, and new modules to be easily added. The basis of the framework is an abstract functional interface that defines the behavior and data to be shared among modules. New formalism and solver modules continue to be added to the tool. This paper describes recent additions to Möbius, including a fault tree model definition formalism, a model composition formalism based on action synchronization, improvements in reward model definition, and additional lumping capabilities in the symbolic state space generator. Möbius ToolMöbius is a discrete-event system analysis tool that has been widely used for the analysis of dependability and performability properties of systems. Recently, Möbius has also been applied to the analysis of system survivability and assurance [1], [2]. Möbius supports multiple modeling formalisms as well as multiple solution techniques. It was created to satisfy the need for a general, common modeling environment to support the development and comparison of new modeling technologies, and avoid the need to continually reinvent and reintegrate older, established technologies. The Möbius framework consists of an abstract functional interface (AFI) [3] that makes it possible for modules to interact with each other in a unified manner.The AFI is implemented by a set of C++ base classes that represent common components of discrete-event models: state variables, actions, and models. State variables hold the state of the model, actions generate events that change the state of the model, and models represent a component in a system and contain sets of actions and state variables.The Möbius tool architecture is designed to be flexible and portable. The front-end of the architecture consists of a Java-based graphical user interface. The back-end is written in C++ to attain efficient execution of the models and high performance for the solution techniques. Modules can either implement model definition formalisms or provide new solution algorithms. New modules can be easily incorporated into the tool to expand the set of available functionalities. Further details on the Möbius framework and tool can be obtained from www.mobius.uiuc.edu. New CapabilitiesSeveral new features have been included in releases of the Möbius tool during the past year. These features include two new model definition formalisms, unified support for reward variables across all solution techniques, support for the evaluation of reward variables at multiple time points, and expanded lumping capabilities within the symbolic state space generator. Model Definition FormalismsSimple systems can often be represented by a single model constructed with a single modeling formalism. For more complex systems, it is often convenient to use hierarchical representations of the system, made by decomposing the system into components, constructing a separate model for all of the components i...
MOQA is a language specifically designed to facilitate average-case execution time analysis. It incorporates some innovative techniques to make this possible. Following on from this, a tool called Distritrack has been built to perform the analysis of MOQA programs, adhering strictly to the language specification.
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