DrawNet++: A Flexible Framework for Building Dependability Models

The DrawNet++ project addresses the compositional construction of dependability models [3, 4]. Its main goals are to provide: a) a GUI to any graph-based formalism; b) a support to the design process of dependability models, according to concepts inspired by object orientation (OO); c) a user friendly front-end for different classes of analysis/simulation tools. Such features enforce the rapid prototyping and the reuse of sub-models. The formalisms adopted to implement the (sub)models may differ, by allowing to study both compositional problems related to the usage of a single specification formalism and interoperability issues within a multiformalism environment. A prototype post-processor has been implemented to interface a few analysis/simulation tools and retrieve/show performance results. By now, Parametric Fault Tree (PFT) [1] and Stochastic Well Formed Nets (SWN)[2], are supported. An XML description of the user defined models is generated by the tool and XSL styles are used to translate the XML representation into a syntax suitable for the specific analysis tool. We use the DrawNet++ framework to build compositional SWN models and models of highly redundant systems by combining PFT with SWN [1]: since state space analysis tools are needed to represent dependencies between components, repair, transient faults etc, we model them by SWN submodels and compose such predefined blocks with a SWN model of the system obtained by automatically translating a PFT model. In this context we use the DrawNet++ a) to define and draw composed models (e.g. PFT and SWN blocks); b) to produce the syntax representation of the entire model and c) to present the results computed by the solvers.