Reachability Tree Method Research Articles

A Mobile-Agent Environment for Service Oriented System using Strong Mobility

In this research, we extended our existing work by applying the concept of strong mobility of mobile agent to make service oriented systems. Initially, an algorithm is developed on the model, based on strong mobility between the clients and server using mobile agent technology via VSAT (very small aperture technology). Where clients are deployed in critical regions which calculate flood discharge based on speed of flood. The proposed algorithm has been verified through the mobile Petri net, a formal language, which is used to formalize it. Reachability tree method of analysis is adopted to verify this model. For practical implementation, a critical area ‘Kalabagh’ is selected and a Java based system is developed of this model. The system is verified by using the historical data values of this critical area and the results verify the model.

Analysis of Flexible Assembly Processes Based on Structural Decomposition of Petri Nets

We propose a controlled assembly Petri net with alternative route (CAPN-AR) model for a class of flexible assembly processes with alternative routes and unreliable resources. Alternative routes significantly enhance the reliability through the routing flexibility of the system. It is not required for a CAPN-AR to be live to maintain production. For this reason, we propose the concept of persistent production for the CAPN-AR. However, alternative routes also add complexity to the analysis of the systems. As the PNs grow rapidly with the scale of the problem, an existing reachability-tree method is feasible only for small nets. We propose an analysis method that can scale with the problems based on structural decomposition of the CAPN-AR. We study the conditions for persistent production, propose a deadlock avoidance algorithm with polynomial complexity for CAPN-AR, and access its robustness property with respect to resource failures.

Design of Traffic Light Control Systems Using Statecharts

Statechart has been utilized as a visual formalism for the modeling of complex systems. It illuminates the features on describing properties of causality, concurrency and synchronization. This paper focuses on the use of statecharts to model an urban traffic lights control system. The applications of statecharts to eight-phase, six-phase and two-phase traffic lights are illustrated. The advantage of the proposed approach is the clear presentation of traffic lights' behaviors in terms of conditions and events that cause the phase alternations. Moreover, the paper also proposes a new modeling methodology, called concurrent state graphs, that allows us to present all the concurrent states in complex statecharts. The analysis of the control models is performed to demonstrate how the models enforce the lights' transitions by reachability tree method. And then the reachability and reversibility properties of the control statecharts will be obtained. Finally, an urban traffic lights' control system with nine intersections will be realized. To our knowledge, this is the first work that employs statecharts to obtain the models of the urban traffic light control system.

Petri net approach to disassembly process planning for products with complex AND/OR precedence relationships

We present a Petri net (PN)-based approach to automatically generate disassembly process plans (DPPs) for product recycling or remanufacturing. We define an algorithm to generate a geometrically-based disassembly precedence matrix (DPM) from a CAD drawing of the product. We then define an algorithm to automatically generate a disassembly Petri net (DPN) from the DPM; the DPN is live, bounded, and reversible. The resulting DPN can be analyzed using the reachability tree method to generate feasible DPPs, and cost functions can be used to determine the optimal DPP. Since reachability tree generation is NP-complete, we develop a heuristic to dynamically explore the v likeliest lowest cost branches of the tree, to identify optimal or near-optimal DPPs. The cost function incorporates tool changes, changes in direction of movement, and individual part characteristics (e.g., hazardous). An example is used to illustrate the procedure. This approach can be used for products containing AND, OR, and complex AND/OR disassembly precedence relationships.

A Petri net synthesis theory for modeling flexible manufacturing systems

A theory that synthesizes Petri nets for modeling flexible manufacturing systems is presented. The theory adopts a bottom-up or modular-composition approach to construct net models. Each module is modeled as a resource control net (RCN), which represents a subsystem that controls a resource type in a flexible manufacturing system. Interactions among the modules are described as the common transition and transition subnets. The net obtained by merging the modules with two minimal restrictions is shown to be conservative and thus bounded. An algorithm is developed to detect two sufficient conditions for structural liveness of the net. The algorithm examines only the net's structure and the initial marking, and appears to be more efficient than state enumeration techniques such as the reachability tree method. In this paper, the sufficient conditions for liveness are shown to be related to some structural objects called siphons. To demonstrate the applicability of the theory, a flexible manufacturing system of a moderate size is modeled and analyzed using the proposed theory.

Analysis of petri nets by partitioning: splitting places or transitions

In this paper, two methods for the analysis of large Petri nets by partitioning are proposed. These methods permit a great saving of computation time and storage. Useless efforts spent in the analysis of large Petri nets are spared by a look to the partitions of interest. It is possible to study the characteristics of the required places by involving them in a partition. It was shown that partitioning preserves the characteristics of the main Petri net. The reachability tree method or the matrix equations approach, which were untractable at the whole net level, may be used at the subnet level to get the needed analysis criteria.

Analysis of Petri nets by partitioning: Splitting transitions

In this paper, a method of analysis of large Petri nets by partitioning is proposed. This method permits a great saving of computation time and storage. Useless efforts spent in the analysis of large Petri nets are spared by a look to the partitions of interest. It is possible to study the characteristics of the required places by involving them in a partition. It was shown that partitioning preserves the characteristics of the main Petri net. The reachability tree method or the matrix equations approach, which were untractable at the whole net level, may be used at the subnet level to get the needed analysis criteria.

A tabular method for the analysis of large petri nets

In this paper, a method of analysis of large Petri nets by partitioning is proposed. This method permits a great saving of computation time and storage, which is specially useful when using mini or microcomputers. It was shown that partitioning preserves the characteristics of the main Petri net. The reachability tree method or the matrix equations approach, which were untractable at the whole net level, may be used at the subnet level to get the needed analysis criteria.