• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.955-958
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• 2002

A workflow is a flow of work supported by computers. An instance of a workflow is called case. Companies need to constantly refine their current workflows in order to meet various requirements. The change of current workflows is called dynamic change of the workflow. Since Ellis et al. proposed three change types, Flush, Abort, and Synthetic Cut-Over in 1995, various change types have been proposed. A promising change type is Migrate proposed by Sadiq et al., because Migrate changes workflow definitions immediately and makes the redo of cases minimum. However, the formal modeling and time-dependent analysis of Migrate has not been done. This paper proposes a method of computing change time of Migrate dynamic changes for time-dependent analysis. Change time is a measure for evaluating dynamic changes. We first show a Petri-nets-based model of Migrate dynamic changes. Then we present a method of computing change time based on the net model. Finally, we apply the method to 270 examples, and show experimental results, and comparison with Ellis et al..'s three change types.

• International Journal of Railway
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• v.2 no.3
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• pp.99-106
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• 2009

Checks and tests before putting safety facilities into service as well as the results of these tests are essential, time consuming and may show great variations between each other. Economic constraints and the increasing complexity associated with the development of computerized tools tend to limit the capacity of the classic approval process (manual or automatic). A reduction of the validation cover rate could result in practice. This is not compatible with the French national plan to renew the interlocking systems of the national network. The method and the tool presented in this paper makes it possible to formally validate new computerized systems or evolutions of existing French interlocking systems with real-time functional interpreted Petri nets. The aim of our project is to provide SNCF with a method for the formal validation of French interlocking systems. A formal proof method by assertion, which is applicable to industrial automation equipment such as interlocking systems, and which covers equally the specification and its real software implementation, is presented in this paper. With the proposed method we completely verify that the system follows all safety properties at all times and does not show superfluous conditions: it replaces all the indoor checks (not the outdoor checks). The advantages expected are a significant reduction of testing time and of the related costs, an increase of the test coverage rate, an answer to the new demand of railway infrastructure maintenance engineering to modify and validate computerized interlocking systems. Formal methods mastery by infrastructure engineers are surely a key to prove that more safety is not necessarily more expensive.

• The KIPS Transactions:PartC
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• v.8C no.1
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• pp.97-104
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• 2001

In this paper, we present a new hierarchical model for performance analysis of channel allocation and packet service protocol in wireless n network. The proposed hierarchical model consists of two parts : upper and lower layer models. The upper layer model is the structure state model representing the state of the channel allocation and call service. The lower layer model, which captures the performance of the system within a given structure state, is the wireless packet retransmission protocol model. These models are developed using SRN which is an modeling tool. SRN, an extension of stochastic Petri net, provides compact modeling facilities for system analysis. To get the performance index, appropriate reward rates are assigned to its SRN. Fixed point iteration is used to determine the model parameters that are not available directly as input. That is, the call service time of the upper model can be obtained by packet delay in the lower model, and the packet generation rates of the lower model come from call generation rates of the upper model.

• Management Science and Financial Engineering
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• v.14 no.1
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• pp.23-34
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• 2008

In this study, we consider stationary waiting times in a Poisson driven single-server m-node queues in series. We assume that service times at nodes are independent, and are either deterministic or non-overlapped. Each node excluding the first node has a finite waiting line and every node is operated under a FIFO service discipline and a communication blocking policy (blocking before service). By applying (max, +)-algebra to a corresponding stochastic event graph, a special case of timed Petri nets, we derive the explicit expressions for stationary waiting times at all areas, which are functions of finite buffer capacities. These expressions allow us to compute the performance measures of interest such as mean, higher moments, or tail probability of waiting time. Moreover, as applications of these results, we introduce optimization problems which determine either the biggest arrival rate or the smallest buffer capacities satisfying probabilistic constraints on waiting times. These results can be also applied to bounds of waiting times in more general systems. Numerical examples are also provided.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.9
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• pp.205-214
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• 2012

The main thing that IT operation managers consider is protecting assets of corporation from system failure and disaster. Therefore, this research proposed a backup system for a disaster recovery. Previous backup method is that if database update occurs, this record is saved in redo log, and if the size of record file is over than expected, this file is saved in archive log in order. Thus, it is possible to occur errors of data loss from the process of data backup which change in real time while changes of database occur. Suggested backup system is back redo log up to database of transaction log in real time, and back a record that can be omitted from previous backup method up to archive log. When recover the data, it is possible to recover redo log in real time online, and it minimizes data loss. Also, throughout multi thread processing method data recovery is performed and it is designed that system performance is improved. To verify stability of backup system CPN(Coloured Petri Net) is introduced, and each step of backup system is displayed in diagram form, and th e stability is verified based on the definition and theorem of CPN.