A methodology for formal expression of hierarchy in model solution

A methodology for formal specification of hierarchy both in model specification and model solution is presented. Hierarchy is allowed to exist among different model types used in performance and dependability modeling. This offers a lot of flexibility and power to the modeler. The methodology presents a unified view of a variety of modeling techniques such as hierarchical composition, behavioral decomposition, iterative hierarchical modeling, reward-based performability modeling, aggregation, etc. This methodology brings the hierarchical modeling technique(s), based on which the model is constructed, to the fore. The results in a better understanding of the model by the user and it can simplify model validation if need be. Such a methodology would also make the design of modeling toolkits, which allow these modeling techniques, much simpler by presenting a conceptually simpler and unified view of a variety of modeling techniques. The formal expression is also expected to assist the modeler in construction of large, complex models