The new version of QPN-Tool supports the specification and efficient analysis of hierarchically combined Queueing Petri nets (HQPNs).
It attacks the two major problems of model-based system analysis:
Largeness of model specifications: HQPNs combine coloured GSPNs,
queueing networks and offer hierarchical specification facilities.
This yields specification advantages which result in a compact model
specification: from coloured GSPNs we obtain simple description methods
for synchronisation, fork and join-operations, from queueing
networks we gain natural description methods for queues and
scheduling strategies and finally the hierarchical approach results
in the capability of reusing submodels and of keeping a clear and structured
design. The specification of HQPNs is encouraged in QPN-Tool by a
convenient graphical user interface. Even novice users get
quickly acquainted with HQPNs. A simple and convenient specification
technique is very important for increasing user acceptance
[22].
Largeness of state spaces: Quantitative analysis, especially
numerical analysis of finite Markov chains, notoriously suffers from
the so-called state space explosion problem. Modern tensor based
iteration techniques extend the set of solvable state spaces by
about one order of magnitude. This is possible if the model is
structured adequately. QPN-Tool manages to exploit the hierarchical
structure obtained by the hierarchical modelling specification for a
structured, tensor based quantitative analysis.
A further advantage of HQPNs is that they combine the description of qualitative and quantitative system aspects in one modelling formalism. QPN-Tool supports these directions and again exploits the hierarchical structure of the model. It offers qualitative analysis algorithms based on Petri net theory for a so-called local analysis of isolated subnets and for a global analysis of a complete HQPN. This assists a user to identify well-defined parts/modules of his system and it especially facilitates error recognition.
Altogether QPN-Tool combines several modelling formalisms into a formalism, which is supported by a convenient graphical user interface, and combines qualitative and quantitative analysis techniques, which are able to exploit the hierarchical structure given by a model specification.
Future developments of the QPN-Tool are dedicated to the integration of simulative techniques. Further prospects concern exact and approximate aggregation techniques based on the hierarchical description and the exploitation of model symmetries. The integration of immediate queueing places [2] and queues with further scheduling strategies is planned as well [5]. At present the graphical user interface is being recoded for the X Window system.