This paper presents the Coloured Petri Net modeling for security analysis of the Extended Role Based Access Control systems.

This paper proposes methods of computing maximum throughput for Petri nets that model workflows including resources, called WF-nets with resources. We first propose the formal definitions of WF-nets with resources and their subclasses: marked graph/state machine WF-nets with conflict-free resources (CF-Res-MG/SMWF-nets). We also show several properties of CF-Res-MG/SMWF-nets. Next we give the methods of computing maximum throughput for CF-Res-MG/SMWF-nets under condition that all tokens have to be processed in the order of First-In First-Out (FIFO). Concretely, for CF-Res-MGWF-nets, on the basis of Ramamoorthy's method of computing cycle time, we give an algorithm of computing maximum throughput under the FIFO condition. For CF-Res-SMWF-nets, there is not any method of computing maximum throughput under the FIFO condition. So we are the first to give an algorithm of computing maximum throughput for CF-Res-SMWF-nets under the FIFO condition. Finally we show an example of computing maximum throughput by using our method.

Through many researches on modeling and analyzing biological pathways, Petri net has recognized as a promising method for representing biological pathways. Recently, Matsuno et al. (2003) introduced hybrid functional Petri net (HFPN) for giving more intuitive and natural biological pathway modeling method than existing Petri nets. They also developed Genomic Object Net (GON) which employs the HFPN as a basic architecture. Many kinds of biological pathways have been modeled with the HFPN and simulated by the GON. This paper gives a new HFPN model of "cell cycle of fission yeast" with giving six basic HFPN components of typical biological reactions, and demonstrating the method how biological pathways can be modeled with these HFPN components. Simulation results by GON suggest a new hypothesis which will help biologist for performing further experiments.

This paper addresses the scheduling problem of a class of automated manufacturing systems with multiple resource requests. In the automated manufacturing system model, a set of jobs is to be processed and each job requires a sequence of operations. Each operation may need more than one resource type and multiple identical units with the same resource type. Upon the completion of an operation, resources needed in the next operation of the same job cannot be released and the remaining resources cannot be released until the start of the next operation. The scheduling problem is formulated by Timed Petri nets model under which the scheduling goal consists in sequencing the transition firing sequence in order to avoid the deadlock situation and to minimize the makespan. In the proposed genetic algorithm with deadlock-free constraint, Petri net transition sequence is coded and a deadlock detection method based on D-siphon technology is proposed to reschedule the sequence of transitions. The enabled transitions should be fired as early as possible and thus the quality of solutions can be improved. In the fitness computation procedure, a penalty item for the infeasible solution is involved to prevent the search process from converging to the infeasible solution. The method proposed in this paper can get a feasible scheduling strategy as well as enable the system to achieve good performance. Numerical results presented in the paper show the efficiency of the proposed algorithm.

A batch process is a typical concurrent system in which multiple interacting tasks are carried out in parallel on several batches at the same time. A major difficulty in designing a batch control system is the lack of modeling techniques. This paper aims at developing a method of constructing batch control system models in a hierarchical manner and operating batch processes using the constructed models. For this purpose, it first defines process and plant specifications described by partial languages, next presents a procedure for constructing hierarchical Petri net based models, and states the verification of models based on reachability analysis. It also discusses the detection of faults and conflicts in batch processes based on place-invariant analysis.

In this paper, introducing a stochastic hill-climbing dynamics into an optimal competitive Hopfield network model (OCHOM), we propose a new algorithm that permits temporary energy increases, which helps the OCHOM escape from local minima. In graph theory, a clique is a completely connected subgraph and the maximum clique problem (MCP) is to find a clique of maximum size of a graph. The MCP is a classic optimization problem in computer science and in graph theory with many real-world applications, and is also known to be NP-complete. Recently, Galan-Marin et al. proposed the OCHOM for the MCP. It can guarantee convergence to a global/local minimum of energy function, and performs better than other competitive neural approaches. However, the OCHOM has no mechanism to escape from local minima. The proposed algorithm introduces stochastic hill-climbing dynamics which helps the OCHOM escape from local minima, and it is applied to the MCP. A number of instances have been simulated to verify the proposed algorithm.

This letter describes the design and performance of a new ATM Adaptation Layer (AAL-UDP) for time-critical traffic over wireless ATM networks. The key ideas in the design consist of no discard at the AAL level and header protection with sequence number mechanism. The UDP/IP header is repeated for reliability, because it contains the most important information such as address and port number. The simulation results show that the AAL-UDP provides significant improvement in throughput as well as in application-level performance compared to the conventional AAL 5 case.

Using a level oriented model for verification of asynchronous circuits helps users to easily construct formal models with high readability or to naturally model data-path circuits. On the other hand, in order to use such a model for larger circuit, some technique to avoid the state explosion problem is essential. This paper first defines a level oriented formal model based on time Petri nets, and then proposes a partial order reduction algorithm that prunes unnecessary state generation while guaranteeing the correctness of the verification.

In databases based on a multi-aspects object data model whcih enables multiple aspects of a real-world entity to be represented and to be acquired/lost dynamically, Object Migration (OM) updating membership relationships between an object and classes occurs, as the properties of the object evolve in its lifetime. We have proposed an OM behavior modeling framework using Colored Petri Nets (CPN) to analyze OM behavior. Based on the proposed framework, this paper presents a technique for constructing OM behavior models from OM constraint descriptions and class schemas as its input. The presented technique makes it easy to construct consistent and complete OM behavior models, since OM constraints are described in a simple, modular, and declarative form.

The paper develops the transformation rules in order to use the Stochastic Petri Net model to evaluate the performance of various task scheduling algorithms. The transformation rules are applied to DFRN scheduling algorithm to investigate its effectiveness. The performance comparison reveals that the proposed approach provides very accurate evaluation for the scheduling algorithm when the Communication to Computation Ratio value is small.

Finding a nonnegative integer solution x for Ax = b (A Zmn, b Zm1) in Petri nets is NP-complete. Being NP-complete, even algorithms with theoretically bad worst case and with average complexity can be useful for a special class of problems, hence deserve investigation. Then a Grobner basis approach to integer programming problems was proposed in 1991 and some symbolic computation systems became to have useful tools for ideals, varieties, and algorithms for algebraic geometry. In this letter, Grobner basis approach is applied to three typical problems with respect to state equation in P/T Petri nets. In other words, after Grobner bases are derived by the tool Maple 7, we consider how to derive the T-invariants and particular solutions of the Petri nets by using them in this letter.

Progress in WDM transmission technology and the development of optical cross-connect systems has made optical backbone networks a reality. The conventional planning methodologies for such optical backbone networks calculate optimum light-path arrangements to minimize the network cost under the condition that the number of demanded light-paths is given in advance. However, the light-path demand varies according to the light-path prices. Thus, a new planning methodology for the optical backbone networks is necessary to optimize the light-path prices and to maximize the profit obtained from the network. This paper proposes a new planning methodology for the survivable optical networks. This methodology is based on economic theory for competitive markets involving plural kinds of commodities. Using this methodology, the optimum light-path prices can be decided to maximize the obtained profit. A numerical example is presented to show that the obtained profit can be improved by preparing various light-path classes with different recovery modes and introducing an appropriate light-path pricing according to the reliability of each light-path class.

The forbidden state problem is to synthesize a control policy for preventing a Petri net from reaching any state in its forbidden set. In this paper, we address a liveness preserving version of the forbidden state problem for lossy Petri nets. During the process of keeping Petri nets out of the set of their forbidden states, a control policy does not disable a live marking. We present a method to solve the above problem based on fixed point computations. We show that for lossy Petri nets, the problem is decidable. From a practical viewpoint, the problem associated with our fixed point approach is 'state explosion. ' In order to overcome this problem, we propose a symbolic approach, which uses Boolean functions for implicitly representing the set of states. We use Boolean functions for representing reachable markings. Thus OBDDs, compact representations of Boolean functions, can reduce the time and space involved in solving the forbidden state problem described in this paper.

This paper discusses formal modeling and performance evaluation for a type of dynamic change of workflow, called Migrate. Workflow means the flow of work and is designed to process similar instances, called cases. Companies need to continuously refine their current workflow in order to adapt them to various requirements. The change of a current workflow is called dynamic change of the workflow. Before changing a workflow, there exist cases in the workflow. If these cases are ignored or fall into deadlock, the changed workflow would become inconsistent. Since Ellis et al. proposed three change types, Flush, Abort, and Synthetic Cut-Over that keep consistency of workflows in 1995, various change types have been proposed, in which there is a promising change type called Migrate that is proposed by Sadiq et al. Sadiq et al. proposed the concept of Migrate, but did not give a formal model of Migrate. Meanwhile, we have proposed a measure, called change time, in order to evaluate dynamic change of workflows, and used this measure to evaluate the performance on change time for Ellis et al. 's three change types. However, the performance evaluation on change time for Migrate has not been done. In this paper, we first give a Petri-nets-based model of Migrate. Then we present a method of computing change time based on the net model. Finally, we apply the method to 270 examples and show the comparison results between Migrate and Ellis et al. 's three change types.

Caching web files reduces user response time as well as network traffic. When implementing caches, the file caching problem must be addressed; the problem is how to determine which files should be evicted from a cache when there is insufficient space for storing a new file so that the sum of the mis-hit (fault) file costs is minimized. Greedy-Dual-Size (GDS) is the best online algorithm in terms of competitiveness, i. e. , (k)/(k-h+1)-competitive, where k and h are the storage space of, respectively, GDS and an optimal offline algorithm. GDS performs very well even in trace-driven simulations. The worst-case time taken to service a request is another important measure for online file caching algorithms since slow response times render caching meaningless from the client's view point. This paper proposes a fast randomized (k)/(k-h+1)-competitive algorithm that performs in O(2log ^* k) time per file eviction or insertion, whereas GDS takes O(log k) time, where 2log ^* k is a much slower increasing function than log k. To confirm its practicality, we conduct trace driven simulations. Experimental results show that our algorithm attains only slightly worse byte hit rates and sufficiently large reduced latency in comparison with GDS, and our algorithm is a good candidate for caches requiring high-speed processing such as second-level caches in the large networks.

This paper presents a dynamic node decaying method (DNDM) for layered artificial neural networks that is suitable for classification problems. Our purpose is not to minimize the total output error but to obtain high generalization ability with minimal structure. Users of the conventional back propagation (BP) learning algorithm can convert their program to the DNDM by simply inserting a few lines. This method is an extension of a previously proposed method to more general classification problems, and its validity is tested with recent standard benchmark problems. In addition, we analyzed the training process and the effects of various parameters. In the method, nodes in a layer compete for survival in an automatic process that uses a criterion. Relatively less important nodes are decayed gradually during BP learning while more important ones play larger roles until the best performance under given conditions is achieved. The criterion evaluates each node by its total influence on progress toward the upper layer, and it is used as the index for dynamic competitive decaying. Two additional criteria are used: Generalization Loss to measure over-fitting and Learning Progress to stop training. Determination of these criteria requires a few human interventions. We have applied this algorithm to several standard benchmark problems such as cancer, diabetes, heart disease, glass, and iris problems. The results show the effectiveness of the method. The classification error and size of the generated networks are comparable to those obtained by other methods that generally require larger modification, or complete rewriting, of the program from the conventional BP algorithm.

This paper presents a new hierarchical scheduling method for a large-scale manufacturing system based on the hybrid Petri-net model, which consists of CPN (Continuous Petri Net) and TPN (Timed Petri Net). The study focuses on an automobile production system, a typical large-scale manufacturing system. At a high level, CPN is used to represent continuous flow in the production process of an entire system, and LP (Linear Programming) is applied to find the optimal flow. At a low level, TPN is used to represent the manufacturing environment of each sub-production line in a decentralized manner, and the MCT algorithm is applied to find feasible semi-optimal process sequences for each sub-production line. Our proposed scheduling method can schedule macroscopically the flow of an entire system while considering microscopically any physical constraints that arise on an actual shop floor.

In narrow band power-line communication (PLC) systems, which use frequency band below a few hundred kHz, the noise on power-line is non-white and non-stationary. Under such environment, the performance of Orthogonal Frequency Division Multiplex (OFDM) modulation system is analyzed, and time and frequency dependence of bit error rate (BER) is clarified. In addition, the possibility of performance improvement with the symbol level repetition coding employing cyclo-stationary feature of power-line noise is presented.

A siphon-trap of a Petri net N is defined as a place set S with S = S, where S = { u| N has an edge from u to a vertex of S} and S = { v| N has an edge from a vertex of S to v}. A minimal siphon-trap is a siphon-trap such that any proper subset is not a siphon-trap. The following polynomial-time algorithms are proposed: (1) FDST for finding, if any, a minimal siphon-trap or even a maximal class of mutually disjoint minimal siphon-traps of a given Petri net; (2) FDSTi that repeats FDST i times in order to extract more minimal siphon-traps than FDST. (3) STFM_T (STFM_Ti, respectively) which is a combination of the Fourier-Motzkin method and FDST (FDSTi) and which has high possibility of finding, if any, at least one minimal-support nonnegative integer invariant.

This paper develops a framework to support trace theoretic verification of timed circuits and systems. A theoretical foundation for classifying timed traces as either successes or failures is developed. The concept of the semimirror is introduced to allow conformance checking thus supporting hierarchical verification of timed circuits and systems. Finally, we relate our framework to those previously proposed for timing verification.