A FRAMEWORK FOR MODELING DEPENDABLE REAL-TIME DISTRIBUTED SYSTEMS

A systematic way to introduce fault-tolerant and time-dependent proper ties into a complex software system is presented. The approach is base d on an extended Petri Net model, called the G-Net, enhanced with a de terministic timing scheme. In the Timed G-Net (TGN) model, exception h andling and timing mechanisms are used to introduce fault-tolerant and real-time properties. The basic idea is to use basic building blocks with timing properties to allow objects to treat a timing error by rai sing an exception and triggering some corrective actions. Using TGNs a s these basic building blocks, we further refine the model into a Smar t Object (SMO) model. In each SMO, a TGN specification associated with a set of attributes, monitor/error-handler links and protocols suppor t the construction of more reliable applications through an automatic transformer. This framework can contribute to alleviating the burden o n the developers in designing a complex real-time dependable system. W e use examples to show that a simplified real-time distributed air tra ffic control system can be modelled effectively using the SMO model.