Using a timed Petri net (TPN) to model a bank ATM

This paper explains how a working Petri Net model developed for a soft real time system. A bank ATM connects to an ATM controller, which in turn connects to a card authorization system. This model is developed using timed Petri nets and there is the addition of other complex mechanisms that give more realistic behavior and a finer level of detailed events. More complex constructs like: timers, reset points, transaction timeouts, redundancy mechanisms and others are included. First we discuss how the model was built using a bottom up approach. Each of the main components of the system are identified and built using Petri nets. These are tested in isolation and then the complete system is assembled. This is similar to a bottom up approach. Once that the main model is built it is implemented on a simulation tool and used to derive performance results for the system. The final model is live and exhibits repetitive, consistent behavior. Results data have been included in tabular form and depicted graphically. These data show how it is possible to derive results for software and hardware performance using Petri Nets. This is quite exclusive because most software development methods like the UML and even formal techniques do not give us performance analysis and neither proper features for redundancy. To conclude it is possible to say that if good Petri Net simulation tools are available it is possible to use Petri Nets to describe soft real time systems in fine detail and analyze them. At present this cannot be easily achieved by many other techniques when the system involved has stringent synchronization requirements and timing constraints. The work presented here can be further developed