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This talk will present two detailed examples of hybrid systems, covering design, simulation and implementation. The first concerns an Automated Highway System. The second application deals with a collection of autonomous unmanned aircraft. The paper provides a background about hybrid systems.
We present a new technique for the generation and storage of the reachability set of a Petri net. Our approach is inspired by previous work on Binary and Multi-valued Decision Diagrams but exploits a concept of locality for the effect of a transition’s firing to vastly improve algorithmic performance. The result is a data structure and a set of manipulation routines that can be used to generate and...
Symbolic techniques based on BDDs (Binary Decision Diagrams) have emerged as an efficient strategy for the analysis of Petri nets. The existing techniques for the symbolic encoding of each marking use a fixed set of variables per place, leading to encoding schemes with very low density. This drawback has been previously mitigated by using Zero-Suppressed BDDs, that provide a typical reduction of BDD...
Stubborn sets aree a tool for state space reduction preserving certain system properties. We present stubborn set approaches for all popular Petri net standard properties. This extends the list of properties that can be analysed successfully (including boundedness, reversibility). For other properties, our approach can lead to larger reductions (reachability) than previous ones. Futhermore, shortest...
CORBA is a standard proposed by the Object Management Group (OMG) in order to promote interoperability between distributed object systems. CORBA provides a programming-language neutral Interface Definition Language (IDL) that describes the syntactic aspects of services supported by remote objects. However, CORBA IDL does not provide any means to specify the behaviour of objects in an abstract and...
In order to widen the applicability of Coloured Petri Nets for the specification and design of large scale distributed applications, a framework has been developed that supports the interaction of Design/CPN and Java processes. The underlying architecture can be used for other tools. Thereby a seamless embedding of the two worlds of Petri nets and object-oriented programming is achieved, allowing...
Recent research in hybrid dynamic systems has brought together formalisms and techniques from computer science and control theory to address problems involving a mixture of discrete and continuous state variables. Computer scientists have extended standard models of finite-state systems to include continuous dynamics that determine when discrete state transitions can occur. Control theorists have...
Discrete event dynamic systems may have extremely large state spaces. For their analysis, it is usual to relax the description by removing the integrality constraints. Applying this idea, continuous P/T systems are defined by allowing fractional firings of transitions, and thus the existence of non-discrete markings [4,5,1]. In this paper we compare the behaviors of discrete and continuous systems,...
The ODP Trader provides a match—;making service for Objects in an Open Distributed System. In previous work, a model of the Trader was created using Coloured Petri Nets, incorporating its capacity for standalone and co-operative Interworking amongst multiple Trader instances. In this paper, the CPN model of the Trader is analysed using Equivalence Classes (for Occurrence Graph reduction) when the...
This paper presents parallel approaches to the complete transient numerical analysis of stochastic reward nets (SRNs) for both shared and distributed-memory machines. Parallelization concepts and implementation issues are discussed for the three main analysis steps that are (1) generation of the underlying continuous-time Markov chain (CTMC), (2) solving the CTMC numerically for the desired time points...
The use of formal methods for specification and analysis of dependable systems is considered a promising opportunity to support the evaluation of critical issues since the early design phases. Stochastic Petri nets can play an important role not only for the specification of functional issues of a system, but also for the predictive evaluation of performance and dependability properties. In this paper...
In this paper we discuss a methodology for monitoring failures and other activity in discrete event systems that are described by Petri nets. Our method is based on embedding the given Petri net model in a larger Petri net that retains the functionality and properties of the given one, perhaps in a non-separate (that is, not immediately identifiable) way. This redundant Petri net embedding introduces...
Embedded system design requires the use of efficient scheduling policies to execute on shared resources, e.g. the processor, algorithms that consist of a set of concurrent tasks with complex mutual dependencies. Scheduling techniques are called static when the schedule is computed at compile time, dynamic when some or all decisions are made at run-time. The choice of the scheduling policy mainly depends...
The model of recursive Petri nets (RPNs) has been introduced in the field of multi-agent systems in order to model flexible plans for agents. In this paper we focus on some theoretical aspects of RPNs. More precisely, we show that this model is a strict extension of the model of Petri nets in the following sense: the family of languages of RPNs strictly includes the union of Petri net and Context...
The paper deals with the computation of flows in coloured nets and with the potential reachability of markings over the integers in p/t nets. We introduce Artin nets as a subclass of coloured nets, which can be handled by methods from Commutative Algebra. As a first result we develop an algorithm for the explicit computation of flows in Artin nets, which is supported by existing tools. Concerning...
The 10th Hilbert problem is used as a test for undecidability of reachability problem in some classes of Petri Nets, such as self-modifying nets, nets with priorities and nets with inhibitor arcs. Common method is proposed in which implementing in a weak sense the multiplication in a given class of Petri nets including PT-nets is sufficient for such undecidability.
Petri Nets have been popular among the developers of workflow management systems for more than twenty years [5]: even if we do not consider the early work of Petri himself and Anatol Holt on modelling procedures with Petri Nets, Paul Zisman and Clarence Ellis adopted Petri Nets for modelling workflows in the late seventies. From those early years, there has been a growing amount of proposals adopting...
The synthesis problem is to decide for a deterministic transition system whether a Petri net with an isomorphic reachability graph exists and in case to find such a net (which must have the arc-labels of the transition system as transitions). In this paper, we weaken isomorphism to some form of bisimilarity that also takes concurrency into account and we consider safe nets that may have additional...
We present a new class of nets which includes and extends both Coloured Nets and Fifo Nets by defining weights on edges and markings of places as traces on a concurrent (trace) alphabet. Considering different independence relations on the alphabet, from the maximal one to the empty one (yielding words), Trace Channel Nets open a hierarchy of semantics on a single net structure. Furthermore a field...
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