Supporting adaptive learning in hypertext environments: a high level timed Petri net-based approach

The work described in this paper is concerned with modeling and analysing distributed object-oriented real time (RT) systems, developed according to DART — Distributed Architecture for Real Time — which provides an object-oriented life cycle for RT systems. The paper first gives an overview of DART, then discusses the usefulness of mapping DART systems onto high level Petri nets as part of an iterative design process. The resultant framework is a modular operational model, based on a powerful Petri nets tool which delivers both the user-interface utilised for animation purposes and a set of mechanisms suited for the analysis of time-dependent behaviour.Keywordsreal timescheduling analysisdistributed systemsobject-orientationPetri netsanimationexecutable specifications

When designing complex systems, mechanisms for structuring, composing, and reusing system components are crucial. Today, there are many approaches for equipping Petri nets with such mechanisms. In the context of defining a standard interchange format for Petri nets, modular PNML was defined as a mechanism for modules in Petri nets that is independent from a particular version of Petri nets and that can mimic many composition mechanisms by a simple import and export concept. Due to its generality, the semantics of modular PNML was only informally defined. Moreover, modular PNML did not define which concepts could or should be subject to import and export in high-level Petri nets. In this paper, we formalise a minimal version of modular high-level Petri nets, which is based on the concepts of modular PNML. This shows that modular PNML can be formalised once a specific version of Petri net is fixed. Moreover, we present and discuss some more advanced features of modular Petri nets that could be included in the standard. This way, we provide a formal foundation and a basis for a discussion of features to be included in the upcoming standard of a module concept for Petri nets in general and for high-level nets in particular.

High level Petri nets (HLPNs) have been widely applied to model concurrent and distributed systems in computer science and many other engineering disciplines. However, due to the expressive power of HLPNs, they are difficult to analyze. In recent years, a variety of new analysis techniques based on model checking have been proposed to analyze high level Petri nets in addition to the traditional analysis techniques such as simulation and reachability (coverability) tree. These new analysis techniques include (1) developing tailored model checkers for particular types of HLPNs or (2) leveraging existing general model checkers through model translation where a HLPN is transformed into an equivalent form suitable for the target model checker. In this paper, we present a term rewriting approach to analyze a particular type of HLPNs -- predicate transition nets (PrT nets). Our approach is completely automatic and implemented in our tool environment, where the frontend is PIPE+, a general graphical editor for creating PrT net models, and the backend is Maude, a well-known term rewriting system. We have applied our approach to the Mondex system -- the 1st pilot project of verified software repository in the worldwide software verification grand challenge, and several well-known problems used in the annual model checking contest of Petri net tools. Our initial experimental results are encouraging and demonstrate the usefulness of the approach.

Qualitative model based verification of operating procedures by high level petri nets

In this paper, we introduce a framework composed of a syntax and its compositional Petri net semantics, for the specification and verification of properties (like authentication) of security protocols. The protocol agents (e.g., an initiator, a responder, a server, a trusted third party, ...) are formalized as roles, each of them having a predefined behavior depending on their global and also local knowledge (including for instance public, private and shared keys), and may interact in a potentially hostile environment. The main characteristics of our framework, is that it makes explicit, structured and formal, the usually implicit information necessary to analyse the protocol, for instance the public and private contextof execution. The roles and the environment are expressed using SPL processes and compositionally translated into high-level Petri nets, while the context specifying the global and local knowledge of the participants in the protocol is used to generate the corresponding initial marking (with respect to the studied property). Finally, this representation is used to analyse the protocol properties, applying techniques of simulation and model-checking on Petri nets. The complete approach is illustrated on the case study of the Kao-Chow authentication protocol.

Petri net (PN), as a kind of powerful modeling tool for discrete-event dynamic systems, has widely applied in many domains. In this paper, two classes of high-level PN, controlled colored Petri net and controlled hybrid Petri net, are proposed and applied in the unit-commitment (UC) problem for a regional power grid with pumped storage stations. At the same time, the principle of large-scale system decomposition-coordination is applied to solve the problem of optimizing system operation. As a result, the UC problem is further simplified, as well as the algorithm efficiency improved. The proposed solution based on the high-level PN models, dynamic programming and decomposition-coordination theory, provides a new modeling methodology and could result in a superior dispatch plan for a regional power grid. (6 pages)

Formalization of process behavior is a key issue for semantic Web services. However, this bears the disadvantage of clumsy specifications. In this paper we introduce a Petri net based approach to capture the semantics of Web services. It offers a visual modeling technique and means of refinement and composition. The model is very formal allowing for a clear specification of the semantics a process has. We combine ideas from the Petri net community with ideas from the description logic area focusing on ontologies

An integrated reconfiguration performance model for interacting satellite networks is an important tool in analyzing reliability and developing protocols for uninterrupted operation. However, such a quantitative model is not easy to develop since it involves many parameters related to the network’s operation and all the earth-linked operational information communicated through it. The aim of this study is to propose an integrated communication model for a network of interacting satellites using high-level petri nets which permit sub-network reconfiguration without loss of communication ability whenever there are satellite communication faults or full failures. To quantify the Vulnerability, Uncertainty and Probability (VUP) in a network a Stochastic Petri Net (SPN) based model is developed. Three indicators are proposed to determine the VUP definitions in interacting network of satellites. To model the overall reconfiguration schemes of a network of interacting satellites, Colored Petri Nets (CPN) paradigm is used so as to simulate the reconfiguration operation of the integrated Networked Control System (NCS). A modular representation of the interacting satellites with the network in terms of satellites’ subsystems and their interconnection together and through the network is provided. Transmission network is modeled through senders and receivers including packet-data transmission. The four developed reconfiguration methods are used to recover the network in case of partial/ full failures occur in the system. The proposed approaches are then used to study the overall response time of a given NCS in interacting satellites, as well as the delays between the mutual senders and receivers. Simulations of the detailed models show that the networked control performance of the interacting satellites, in particular with reference to any satellite failure, can be improved with inclusion of appropriate monitors within the networked system as represented by sub-networks in the CPN model. The suggested integrated networked control schemes can be used to obtain a fault tolerant reconfiguration for a required network performance.

Petri Nets are tools for the modelling and analysis of the behaviour of systems and analysis of the Petri Net can then reveal important information about the structure and dynamic behaviour of the modelled system. In this article, the author argues that Petri Net concepts (when used qualitatively) are not fundamentally different from those of ANT. For example, the ‘places’ from Petri Nets bear a strong resemblance to the actors in ANT, and the ‘triggers’ or ‘transitions’, are somewhat analogous to ANT’s translations. In modelling, places represent conditions and transitions represent events. Tokens may model the resources or data items that are associated with a place or places. The original research that this article is based on was undertaken using an actor-network framework to develop a model for e-Learning for students with Learning Difficulties. This article explores the qualitative use of Petri Nets to supplement this ANT treatment.

Petri Nets are tools for the modelling and analysis of the behaviour of systems and analysis of the Petri Net can then reveal important information about the structure and dynamic behaviour of the modelled system. In this article, the author argues that Petri Net concepts (when used qualitatively) are not fundamentally different from those of ANT. For example, the ‘places’ from Petri Nets bear a strong resemblance to the actors in ANT, and the ‘triggers’ or ‘transitions’, are somewhat analogous to ANT’s translations. In modelling, places represent conditions and transitions represent events. Tokens may model the resources or data items that are associated with a place or places. The original research that this article is based on was undertaken using an actor-network framework to develop a model for e-Learning for students with Learning Difficulties. This article explores the qualitative use of Petri Nets to supplement this ANT treatment.

This paper is concerned with elementary and high-level Petri nets (coloured Petri nets and predicate/transition nets) and their utility for conceptual modeling of information systems. Particular features of existing net classes are discussed and additional net constructs are proposed for that purpose. Adequate conceptual models, i.e., models which reflect an intended view of an information system without any strange or artifical elements are best obtained if the following features are available to the modeler: (i) places have finite capacities (bounded places), (ii) arc expressions denote sets of variable cardinality, (iii) exclusive and shared use of side-conditions can be specified, (iv) terms denoting the set of all entities of a current marking or a specified subset thereof can be used in transition expressions, (v) static properties can be specified in state-oriented terms and impose restrictions on the dynamic properties specified in transition-oriented terms. The paper presents examples of each one of these desirables features and discusses them against the existing high-level Petri net classes or shows how they can be provided without resorting to so-called extensions.

CORBA is a standard proposed by the Object Management Group (OMG) that promotes interoperability between distributed object systems. Following the standardization of this object-oriented middleware, the OMG has specified a set of Common Object Services (COS) that are meant to serve as the building blocks of distributed CORBA applications. The COSes are specified using CORBA Interface Definition Language (IDL), that describes the syntactic aspects of services supported by remote objects. However, CORBA-IDL does not support specification of the behaviour of objects in an abstract and formal way, and behavioural specification is mostly provided in plain English. To overcome this problem, we have proposed a formal description technique (Cooperative Objects) based on high-level Petri nets, and developed a software support environment. The goal of this paper is to demonstrate that our approach is suited to the formal specification of typical CORBA COS, and presents a Cooperative Object model of the CORBA event service, a COS that provides asynchronous, one-to-many communication between objects. The advantages of dealing with a tool-supported, executable formal notation are detailed, as well as the results that can be obtained through Petri net analysis techniques.Key wordsDistributed systemsbehavioural specificationCORBAhigh-level Petri nets

This paper aims at showing how it is possible to combine the advantages of high-level Petri nets and the B method in order to design safety applications. In the railway critical software domain, safety requirements are obviously severe. Indeed, the passing from an informal specification to a formal one is a crucial point in critical software development. High-level Petri nets combine three important features: a graphical representation, a dynamic behavior and an abstraction of the treatments. The B method allows one to pass from an abstract specification to a concrete implementation. The paper proposes an approach that integrates the structuring and modeling of the system behavior by means of colored Petri nets from semi-formal specifications and the generation of a B abstract specification from this Petri net.

The author presents a tutorial on high-level Petri nets and their applications. The author illustrates the transition firing rule of a high-level Petri net using an example. A high-level net can be considered as a structurally folded version of a regular Petri net, if the number of colors is finite. Thus, a high-level net can be unfolded into a regular Petri net by unfolding each place p into a set of places, one for each color of tokens which p may hold, and by unfolding each transition t into a set of transitions, one for each way that t may fire. The author informally introduces high-level nets through examples. The examples are taken from recent applications of high-level Petri nets to : (1) Horn clause logic programs, (2) four-valued annotated predicate logic, (3) nonmonotonic logic and (4) robot planning.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling and verification of a class of real-time systems by the use of High Level Petri Nets