Petri nets and time modelling

Timed PNs enhance modelling capability of PNs by modifying the basic PN semantics to model temporal relations and constraints of a system. This modification makes their analysis more difficult. For example, the existing techniques for reachability analysis of Time PNs is not well suited for dealing with the end-to-end timing issues, and PN based scheduling makes it difficult to use criteria other than makespan, e.g., tardiness. This paper proposes a class of PNs to model time that improves the current analysis techniques and overcomes these difficulties. Temporal constraints are modelled through arc weights that determine the enabling and firing of transitions to generate its reachability tree used for behavioural analysis as in PNs. All transitions fire instantaneously. Time is represented as a state of the system.