History of TimeNET

The software package DSPNexpress has been developed at the Technische Universität Berlin since 1991, mainly influenced by the tool GreatSPN, and is now maintained at TU Dortmund. It provides a user-friendly graphical interface running under X11 and is especially tailored to the steady-state analysis of deterministic and stochastic Petri nets. For the class of generalised and stochastic Petri nets, steady-state and transient analysis components are available. A refined numerical solution algorithm is used for steady-state evaluation of DSPNs, facilitating parallel computation of intermediate results. Isolated components and isomorphisms of subordinated Markov chains of deterministic transitions are detected and exploited.

The first version of TimeNET was a major revision of DSPNexpress at TU Berlin. It contains all analysis components of the latter at that time, but supports the specification and evaluation of eDSPNs. Expolynomially distributed firing delays are allowed for transitions. Different solution algorithms can be used, depending on the net class. If the transitions with non-exponentially distributed firing delays are mutually exclusive, TimeNET can compute the steady-state solution. DSPNs with more than one enabled deterministic transition in a marking are called concurrent DSPNs. TimeNET provides an approximate analysis technique for this class. If the mentioned restrictions are violated or the reachability graph is too complex for a model, an efficient simulation component is available in the TimeNET tool. A master/slave concept with parallel replications and techniques for monitoring the statistical accuracy as well as reducing the simulation length in the case of rare events are applied. Analysis, approximation, and simulation can be performed for the same model classes. TimeNET therefore provides a unified framework for modelling and performance evaluation of non-Markovian stochastic Petri nets. Recent enhancements of TimeNET 3.0  include

• an algorithm for the transient analysis of DSPNs
• a component for the steady-state and transient analysis of discrete time deterministic and stochastic Petri nets
• a component especially designed for manufacturing systems, including
  • modelling with hierarchically and coloured stochastic Petri nets
  • independent models for structure and work plans
  • steady-state analysis and simulation
  • model based control
• a completely rewritten graphical user interface (Agnes), which integrates all different net classes and analysis algorithms

The new version TimeNET 4.0 (stable version available since 2007) includes a completely rewritten JAVA graphical user interface and provides support of the Microsoft Windows operating system. It supports a new class of stochastic colored Petri nets (SCPNs). A standard discrete-event simulation has been implemented for the performance evaluation of SCPN models. SCPNs allow arbitrary distributions of firing delays including zero delays, complex token types, global guards, time guards, and marking dependent transition priorities. Petri net classes are defined by an extendable XML schema in TimeNET 4.0 which affects the behavior of the graphical user interface. A model is a well-formed XML document which is validated automatically. Recent enhancements of TimeNET 4.0  include

• a generic graphical user interface in JAVA based on an XML net class representation, easily extendable for most graph-like modeling formalisms
• user interface and evaluation algorithms run under Windows and Linux operating system environments
• modelling and simulation of stochastic colored Petri nets
• graphical display of SCPN simulation results
• independent components for modelling, simulation, analysis, and result output allowing the GUI to be run on a different computer than the analysis modules