Joël Favrel

Hierarchical reduction method for analysis and decomposition of Petri nets

A hierarchical reduction method for Petri nets is proposed. After a brief survey on the existing methods of Petri net reduction, concepts such as reducible subnet, degree of subnet, and macronode are defined. The subnets are partially ordered by the degree of subnet, and thus the reducible subnets can be reduced into the macronodes. A reduced net can be obtained without changing the properties (for example, liveness and boundedness). A sequence of reduction results in a hierarchy of reduced Petri nets that allow easy verification and hierarchical decomposition of the system.

Generalized Petri Net Reduction Method

A reduction method of generalized Petri nets is proposed. This method is a generalization of the reduction method which was previously given by Lee-Kwang and Favrel. The proposed method is defined not on the basis of the dynamic behavior but of the structure of the net, and thus the test of reducible subnet can be done by a deterministic approach. The reduction preserves the properties such as liveness, boundedness, and proper termination, and allows easy analysis of generalized Petri nets.

Collaborative business and data privacy: toward a cyber-control?

The pervasive use of communication and information technologies can be seen as a driving force to develop distributed organisations. As far as collaborative business is concerned, short-term e-collaboration can be developed. In this case, security policies must be integrated in the common business process (BP) organisation so that trusted co-operation can be established. For this purpose we propose to couple a generic authorisation workflow to the business process own workflow and to report all the actions on the shared information systems. Nevertheless, reporting tools can be seen as threats on data privacy. We propose here a multi-level architecture to provide both a sufficient security level and a personal data privacy protection.

An authorization and access control model for workflow

A workflow is a coordinated arrangement of related tasks in an automated process, the systematic execution of which, ultimately achieves some goal. Workflow management systems (WFMSs) are becoming very popular and are being used to support many of the day to day workflows in large organizations. Workflow management systems are used for critical and strategic applications. Since, security is an essential and fundamental part of workflows, the workflow management system has to manage and execute the workflows in a secure way. Security, in a workflow context, involves the implementation of access control security mechanisms to ensure that tasks are performed by authorized subjects only. In this paper we propose a workflow authorization model capable of specifying authorization in such a way that subjects gain access to required objects only during the execution of the task. We build our model over the well known RBAC framework, and that in addition extends RBAC by including new rules in order to be adaptable with workflow context.

Dynamic generation of disassembly sequences

Disassembly for material recovery and environment protection is an increasingly important aspect in the manufacturing industry. Most of the present research works for disassembly focus on the generation of predictive optimal sequences. In fact, the disassembly process is particularly uncertain. Frequent incidents make a predetermined plan unrealistic. In this paper we present a new disassembly method in which the actual sequence of disassembly operations is progressively elaborated during the execution, in function of the real circumstances of the process. New concepts of disassembly operation and sequence equivalence are proposed together with a new representation of disassembly sequence. A decentralised and distributed control system based on a multi-agent technology is presented. The results of experimentation verify system flexibility and reactivity to unpredictable events, particularly disassembly operation failures.

Hierarchical decomposition of Petri net languages

A method for hierarchical decomposition of Petri net languages is proposed. The method provides a hierarchical structure of a dynamic system if the system is modeled by a Petri net and its initial state is given. The method can be used in analyzing the dynamic behavior of systems.

Taking into account the rescheduling problem during the scheduling phase

Abstract The scheduling problem in production management has been studied for a considerable time, and several types of software are used. A problem arises in updating the production planning, or ‘rescheduling’, when an unexpected event occurs in the shop control. Solving this problem is difficult because the implications of such events are usually impossible to forecast. To prevent this problem, we propose to manipulate a set of equivalent schedules during the short time schedule. Then, if an unexpected event prevents realization of a given schedule, it will be possible to find an equivalent one, without full rescheduling. The primary requirement is to find a formal representation of a set of schedules. This has already been explored using CPM graphs with nodes associated to a set of tasks. We propose in this paper to use an extension of such graphs, PQR trees, that represent both precedence and group constraints. We first reiterate the notion of PQR trees. We present methods to take into acc...

Representation of nonstructured concurrency by Petri net languages

The concurrency is classified into two types: structured concurrency and nonstructured concurrency. After showing that the nonstructured concurrency cannot be represented by the conventional notations in the Petri net language, a method to represent such concurrency by the language is proposed. The proposed method allows us to utilize the existing approaches for analyzing properties of a nonstructured concurrency by the Petri net languages. >

Integration of information and knowledge from the engineering activity to the workshop control

Controlling a flexible manufacturing system (FMS) involves the management of various kinds of knowledge about the different components of the workshop and about the manufactured products. In order to provide flexibility and reactivity, the control system should integrate this information (including information from engineering activities) and also suit the workshop management policy. A model that organizes this knowledge dynamically according to contextual points of view is proposed. It relies on cooperative controllers. Each is based both on a specialized view of the knowledge base and a global view of the entire architecture, and epigenetic neural networks. Cooperation between decision systems takes place directly at a knowledge level, which improves reactivity abilities and allows partial consistent answers to be given quite quickly.<<ETX>>

Optimal assembly plan generation: a simplifying approach

The main difficulty in the overall process of optimal assembly plan generation is the great number of different ways to assemble a product (typically thousands of solutions). This problem confines the application of most existing automated planning methods to products composed of only a limited number of components. The presented method of assembly plan generation belongs to the approach called “disassembly” and is founded on a new representation of the assembly process, with introduction of a new concept, the equivalence of binary trees. This representation allows to generate the minimal list of all non-redundant (really different) assembly plans. Plan generation is directed by assembly operation constraints and plan-level performance criteria. The method was tested for various assembly applications and compared to other generation approaches. Results show a great reduction in the combinatorial explosion of the number of plans. Therefore, this simplifying approach of assembly sequence modeling allows to handle more complex products with a large number of parts.