Showing papers on "Process architecture published in 2008"

Comparing the Expressiveness of Timed Automata and Timed Extensions of Petri Nets

Abstract: Time dependant models have been intensively studied for many reasons, among others because of their applications in software verification and due to the development of embedded platforms where reliability and safety depend to a large extent on the time features. Many of the time dependant models were suggested as real-time extensions of several well-known untimed models. The most studied formalisms include Networks of Timed Automata which extend the model of communicating finite-state machines with a finite number of real-valued clocks, and timed extensions of Petri nets where the added time constructs include e.g. time intervals that are assigned to the transitions (Time Petri Nets) or to the arcs (Timed-Arc Petri Nets). In this paper, we shall semi-formally introduce these models, discuss their strengths and weaknesses, and provide an overview of the known results about the relationships among the models.

Quantifying process equivalence based on observed behavior

Abstract: In various application domains there is a desire to compare process models, e.g., to relate an organization-specific process model to a reference model, to find a web service matching some desired service description, or to compare some normative process model with a process model discovered using process mining techniques. Although many researchers have worked on different notions of equivalence (e.g., trace equivalence, bisimulation, branching bisimulation, etc.), most of the existing notions are not very useful in this context. First of all, most equivalence notions result in a binary answer (i.e., two processes are equivalent or not). This is not very helpful because, in real-life applications, one needs to differentiate between slightly different models and completely different models. Second, not all parts of a process model are equally important. There may be parts of the process model that are rarely activated (i.e., ''process veins'') while other parts are executed for most process instances (i.e., the ''process arteries''). Clearly, differences in some veins of a process are less important than differences in the main arteries of a process. To address the problem, this paper proposes a completely new way of comparing process models. Rather than directly comparing two models, the process models are compared with respect to some typical behavior. This way, we are able to avoid the two problems just mentioned. The approach has been implemented and has been used in the context of genetic process mining. Although the results are presented in the context of Petri nets, the approach can be applied to any process modeling language with executable semantics.

Nets with Tokens which Carry Data

Abstract: We study data nets, a generalisation of Petri nets in which tokens carry data from linearlyordered infinite domains and in which whole-place operations such as resets and transfers are possible. Data nets subsume several known classes of infinite-state systems, including multiset rewriting systems and polymorphic systems with arrays. We show that coverability and termination are decidable for arbitrary data nets, and that boundedness is decidable for data nets in which whole-place operations are restricted to transfers. By providing an encoding of lossy channel systems into data nets without whole-place operations, we establish that coverability, termination and boundedness for the latter class have non-primitive recursive complexity. The main result of the paper is that, even for unordered data domains (i.e., with only the equality predicate), each of the three verification problems for data nets without whole-place operations has non-elementary complexity.

Analyzing interacting WS-BPEL processes using flexible model generation

Abstract: We address the problem of analyzing the interaction between WS-BPEL processes. We present a technology chain that starts out with a WS-BPEL process and translates it into a Petri net model. On the model we decide controllability of the process (the existence of a partner process, such that both can interact properly) and compute its operating guideline (a characterization of all properly interacting partner processes). To manage processes of realistic size, we present a concept of a flexible model generation which allows the generation of compact Petri net models. A case study demonstrates the value of this technology chain.

Intuitive Mapping of UML 2 Activity Diagrams into Fundamental Modeling Concept Petri Net Diagrams and Colored Petri Nets

Abstract: This paper describes how UML 2 Activity diagrams can be intuitively translated into Petri net notations. The UML2 specification states that activities are based on Petri net semantics. The transformation of UML 2 Activity diagrams into Petri net semantics have been researched for various reasons. Translating UML activities into Petri nets creates new problems. The Petri net diagrams are (i) more complex (ii) contain more nodes and edges, (iii) unsuitable for visualization by stakeholders. A solution to this problem is to translate the UML activity diagram into a Fundamental Modeling Concepts Petri net diagram compact notation. This can be converted to a colored Petri net (CPN) for execution and validation. A case study taken from a web ordering system activity is used for explaining and illustrating this concept.

Linking modularity with problem solving and coordination efforts

Abstract: We explore the relationship between process architecture decisions, problem solving and coordination efforts during distributed product development, ie, when development work is dispersed across organizational boundaries Process architecture refers to the manner in which the tasks and interfaces within a project are organized so that a project can be executed in an efficient manner The theoretical foundation for our investigation draws upon the information processing (IP) view of product development and transaction cost economics The IP view calls for manipulation of the architecture by making problem-solving tasks modular, such that reducing task interdependencies minimizes the development time The transaction cost view calls for transactional efficiency, for example, reduction in the coordination burden for each productive task We present several measures of modularity based on a design structure matrix (DSM) mapping of the development task structure Then, we analyze the relation between these measures and transactional efficacy and task completion times Our empirical evidence comes from 71 tasks carried out in 11 software development projects Data analyses show that the improvement in the transactional efficacy is associated with increase in task modularity Our results establish that increasing modularity reduces the development time and the coordination effort However, these results also suggest trade-offs: modularity measures do not contribute equally to this gain in efficiency and increasing modularity is negatively associated with the technical problem-solving efforts Copyright # 2008 John Wiley & Sons, Ltd

Processes for Enterprise Application Architecture Management

Abstract: Over the past few decades, the way in which enterprises have performed their business and organizational changes at the level of information systems has for the most part been incomplete and/or unsystematic. Fundamental IT innovations have therefore coincided with the development of heterogeneous application landscapes which are more or less inconsistent with the business and/or process architecture. Explicit management of the application architecture, which forms the interface between the business and the technical view on the information system, is necessary to recreate and preserve consistency. Based on a requirements analysis for enterprise application architecture management and a discussion of related work from literature and practice, this paper proposes processes that are based on three case studies. The proposed processes are evaluated in respect of the specified requirements.

Transactions on Petri nets and other models of concurrency

Abstract: In Memoriam: Carl Adam Petri.- Strategies for Modeling Complex Processes Using Colored Petri Nets.- Applications of Coloured Petri Nets for Functional Validation of Protocol Designs.- Business Process Modeling Using Petri Nets.- Structure Theory of Petri Nets.- Causality in Extensions of Petri Nets.- External Behaviour of Systems of State Machines with Variables.- The Synthesis Problem.- Models from Scenarios.- Discovering Petri Nets from Event Logs.

Nested Petri nets for adaptive process modeling

Abstract: We consider Nested Petri nets (NP-nets), i.e. Petri nets in which tokens can be Petri nets themselves. To increase flexibility and give tools for modeling adaptive processes we extend this formalism by allowing operations on net tokens. We prove decidability of some crucial for verification problems and thus show that, in spite of very flexible structure, NP-nets maintain "good" properties of ordinary Petri nets.

A Symbolic Algorithm for the Synthesis of Bounded Petri Nets

Abstract: This paper presents an algorithm for the synthesis of bounded Petri nets from transition systems. A bounded Petri net is always provided in case it exists. Otherwise, the events are split into several transitions to guarantee the synthesis of a Petri net with bisimilar behavior. The algorithm uses symbolic representations of multisets of states to efficiently generate all the minimal regions. The algorithm has been implemented in a tool. Experimental results show a significant net reduction when compared with approaches for the synthesis of safe Petri nets.

A Model Driven Approach to Represent Sequence Diagrams as Free Choice Petri Nets

Abstract: Model driven development (MDD) aims to promote the role of modeling in software engineering. Enterprise systems and architectures are often modeled via multiple representations. For example UML models are widely used by the designers to capture various viewpoint of the system; while formal models using languages such as CSP, Z and Petri nets are suitable for the analysis. Model transformation techniques developed as a part of MDD can be applied to generate one model from another model automatically. This allows benefiting from the tools and techniques developed and used in multiple languages. This paper presents a method of applying MDD model transformation from UML 2.0 sequence diagrams to Petri nets. The paper shows that the model transformation results in free choice Petri nets. As a result, the low complexity of analysis and the synthesis techniques can be applied to the models of enterprise systems which are captured in UML sequence diagrams.

Automated Verification of Asynchronous Circuits Using Circuit Petri Nets

Abstract: To detect problematic circuit behaviour, such as potential hazards and deadlocks, in a reasonable amount of time a technique is required which would avoid exhaustive exploration of the state space of the system. Many of the existing methods rely on symbolic traversal of the state space, with the use of binary decision diagrams (BDDs) and associated software packages. This paper presents an alternative approach of using a special type of Petri nets to represent circuits. An algorithm for automatic conversion of a circuit netlist into a behaviourally equivalent Petri net is proposed. Once the circuit Petri net is constructed and composed with the provided environment specification, the presence and reachability of troublesome states is verified by using methods based on finite prefixes of Petri net unfoldings. The shortest trace leading to a deadlock or a hazard in the circuit Petri net is mapped back onto the gate-level representation of the circuit, thus assisting a designer in solving the problem. The method has been automated and compared against previously existing circuit verification tools.

On Synchronous and Asynchronous Interaction in Distributed Systems

Abstract: When considering distributed systems, it is a central issue how to deal with interactions between components. In this paper, we investigate the paradigms of synchronous and asynchronous interaction in the context of distributed systems. We investigate to what extent or under which conditions synchronous interaction is a valid concept for specification and implementation of such systems. We choose Petri nets as our system model and consider different notions of distribution by associating locations to elements of nets. First, we investigate the concept of simultaneity which is inherent in the semantics of Petri nets when transitions have multiple input places. We assume that tokens may only be taken instantaneously by transitions on the same location. We exhibit a hierarchy of `asynchronous' Petri net classes by different assumptions on possible distributions. Alternatively, we assume that the synchronisations specified in a Petri net are crucial system properties. Hence transitions and their preplaces may no longer placed on separate locations. We then answer the question which systems may be implemented in a distributed way without restricting concurrency, assuming that locations are inherently sequential. It turns out that in both settings we find semi-structural properties of Petri nets describing exactly the problematic situations for interactions in distributed systems.

Transformations in Reconfigurable Place/Transition Systems

Abstract: Reconfigurable place/transition systems are Petri nets with initial markings and a set of rules which allow the modification of the net during runtime in order to adapt the net to new requirements. For the transformation of Petri nets in the double pushout approach, the categorical framework of adhesive high-level replacement systems has been instantiated to Petri nets. In this paper, we show that also place/transition systems form a weak adhesive high-level replacement category. This allows us to apply the developed theory also to tranformations within reconfigurable place/transition systems.

McMillan's Complete Prefix for Contextual Nets

Abstract: In a seminal paper, McMillan proposed a technique for constructing a finite complete prefix of the unfolding of bounded (ie, finite-state) Petri nets, which can be used for verification purposes Contextual nets are a generalisation of Petri nets suited to model systems with read-only access to resources When working with contextual nets, a finite complete prefix can be obtained by applying McMillan's construction to a suitable encoding of the contextual net into an ordinary net However, it has been observed that if the unfolding is itself a contextual net, then the complete prefix can be significantly smaller than the one obtained with the above technique A construction for generating such a contextual complete prefix has been proposed for a special class of nets, called read-persistent In this paper, we propose an algorithm that works for arbitrary semi-weighted, bounded contextual nets The construction explicitly takes into account the fact that, unlike in ordinary or read-persistent nets, an event can have several different histories in general contextual net computations

From Human Knowledge to Process Models

Abstract: This contribution suggests a novel approach for a systematic generation of a process model in an informal environment. It is based on the claim that the knowledge about the process to be modelled is distributed in several involved people’s minds. Some people have knowledge about the general process where the single activities are on a high level of abstraction and have to be refined. Other people only know something about some detail of the process, i.e., about the refinement of an activity of the general process which defines a subprocess. Moreover, it is assumed that these domain experts can more easily define instances, i.e. runs, of the general process (of a subprocess, respectively) than the process itself. The approach employs new techniques developed for process mining and Petri net synthesis and adapts these techniques to generate processes from example runs. It is based on a formal definition of partially ordered processes, which allows to proceed in a modular way: Subprocesses and general processes are generated independently. Finally, it is argued that the approach is a suitable first step in a general method for process definitions which is followed by validation techniques.

An urban traffic network model by first order hybrid Petri nets

Abstract: The paper proposes a model for real time control of urban traffic networks. A modular framework based on first order hybrid Petri nets models the vehicle flows by a first order fluid approximation. Moreover, the lane interruptions and the signal timing plan controlling the area are described by the discrete event dynamics using timed Petri nets. The proposed model is applied to a real intersection located in Bari, Italy. Simulation of different scenarios shows the technique efficiency: validation is performed by comparison with a previously proposed alternative approach employing colored Petri nets.

Synthesis of Nets with Step Firing Policies

Abstract: The unconstrained step semantics of Petri nets is impractical for simulating and modelling applications. In the past, this inadequacy has been alleviated by introducing various flavours of maximally concurrent semantics, as well as priority orders. In this paper, we introduce a general way of controlling step semantics of Petri nets through step firing policies that restrict the concurrent behaviour of Petri nets and so improve their execution and modelling features. In a nutshell, a step firing policy disables at each marking a subset of enabled steps which could otherwise be executed. We discuss various examples of step firing policies and then investigate the synthesis problem for Petri nets controlled by such policies. Using generalised regions of step transition systems, we provide an axiomatic characterisation of those transition systems which can be realised as reachability graphs of Petri nets controlled by a given step firing policy. We also provide a decision and synthesis algorithm for PT-nets and step firing policies based on linear rewards of steps, where fixing the reward of elementary transitions is part of the synthesis problem. The simplicity of the algorithm supports our claim that the proposed approach is practical.

Algebraic properties of automata associated to Petri nets and applications to computation in biological systems

Abstract: Biochemical and genetic regulatory networks are often modeled by Petri nets. We study the algebraic structure of the computations carried out by Petri nets from the viewpoint of algebraic automata theory. Petri nets comprise a formalized graphical modeling language, often used to describe computation occurring within biochemical and genetic regulatory networks, but the semantics may be interpreted in different ways in the realm of automata. Therefore, there are several different ways to turn a Petri net into a state-transition automaton. Here, we systematically investigate different conversion methods and describe cases where they may yield radically different algebraic structures. We focus on the existence of group components of the corresponding transformation semigroups, as these reflect symmetries of the computation occurring within the biological system under study. Results are illustrated by applications to the Petri net modelling of intermediary metabolism. Petri nets with inhibition are shown to be computationally rich, regardless of the particular interpretation method. Along these lines we provide a mathematical argument suggesting a reason for the apparent all-pervasiveness of inhibitory connections in living systems.

High-Level Petri Nets control modules for service-oriented devices: A case study

Abstract: This paper describes a solution for the control of service-oriented devices based on modular and special adapted high-level Petri nets process description of intra- and inter-control activities The procedure is applied on a case study scenario, corresponding to a real transfer system made of several control devices represented as service-oriented components able to share information between them The high-level Petri Nets are adapted to associable models applicable to describe control processes and sufficient elastic for different control strategies Valuable and flexible control features are obtained from its application, such as an integrated methodology for the modular control with decision support and validation

Preserving Languages and Properties in Stepwise Refinement-Based Synthesis of Petri Nets

Abstract: The current stepwise refinement operation of Petri nets mainly concentrates on property preservation, which is an effective way to analyze and verify complex systems. Further steps into this field are needed from the perspective of system synthesis and language preservation. First, the refinement of Petri nets is introduced based on a k-well-behaved Petri net, in which k tokens can be processed. Then, according to the different compositions of subsystems, well-, under- and overmatched refined Petri nets are proposed. In addition, the language and property relationships among sub-, original, and refined nets are studied to demonstrate behavior characteristics and property preservation in a system synthesis process. A manufacturing system is given as an example to illustrate the effectiveness of the proposed approach in synthesizing and analyzing the Petri nets of complex systems.

Quickly prototyping petri nets tools with SNAKES

Abstract: This paper presents the toolkit SNAKES that is aimed at providing a flexible solution to the problem of quickly prototyping Petri nets tools In particular, SNAKES is expected to have as few built-in limitations as possible with respect to the particular variant of Petri net to be used The goal is to make SNAKES suitable for any kind of Petri net model, including new ones for which there exists no available tool For this purpose, SNAKES is designed as a very general Petri net core library enriched with a set of extension modules to provide specialised features On the one hand, the core library is versatile in that it defines a general Petri net structure where all the computational aspects are delegated to an interpreted programming language On the other hand, the extension modules provide with enough flexibility to allow to redefine easily any part of the base Petri net model SNAKES is released under the GNU LGPL, it can be downloaded at 〈http://wwwuniv-paris12fr/lacl/pommereau/soft/snakes〉 with the API documentation and a tutorial

Synthesis of Petri Nets from Scenarios with VipTool

Abstract: The aim of this tool paper is twofold: First we show that VipTool [9,2] can now synthesize Petri nets from partially ordered runs. To integrate this extension and further new functionalities, we changed the architecture of VipTool to a flexible plug-in technology. Second we explain how VipTool including the synthesis feature can be used for a stepwise and iterative formalization and validation procedure for business process Petri net models. The synthesis functionalities fill a gap in a previously defined procedure [9,7] where the first definition of an initial process model had to be done "by hand", i.e. without any tool support.

Modelling and verification of timed interaction and migration

Abstract: We present a process algebra where timeouts of interactions and adaptable migrations in a distributed environment with explicit locations can be defined. Timing constraints allow to control the interaction (communication) between co-located mobile processes, and a migration action with variable destination supports flexible movement from one location to another. We define an operational semantics, and outline a structural translation of the proposed process algebra into operationally equivalent finite high level timed Petri nets. The purpose of such a translation is two fold. First, it yields a formal semantics for timed interaction and migration which is both compositional and allows to deal directly with concurrency and causality. Second, it should facilitate the use of simulation and verification tools developed within the area of Petri nets.