Many noticeable studies have focussed on scheduling flat transactions in a distributedreal-time database system (RTDBS). However, a nested transaction model has been widely adopted in many real-life applications such...
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Many noticeable studies have focussed on scheduling flat transactions in a distributedreal-time database system (RTDBS). However, a nested transaction model has been widely adopted in many real-life applications such as Internet stock trading systems and telecommunications. This work concerns efficiently schedulingreal-time nested transactions in a distributed RTDBS. A new real-time scheduler called flexible high reward for nested transactions (FHRN) is proposed. FHRN consists of (1) FHRNp1 policy to schedule real-time nested transactions and (2) 2PL HPN to resolve the concurrent data-accessing problem among interleaved nested transactions. Simulation results show that FHRN outperforms these existent real-time schedulers such as random priority (RP), earliest deadline (ED), highest value (HV), hierarchical earliest deadline (HED), and highest reward and urgency (HRU) when an application requires a nested transaction model.
In this paper, we propose a new approach for controlling the traffic at isolated intersections. We assume that all vehicles are equipped with on-board units (ITS station) that make them able to wirelessly negotiate th...
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In this paper, we propose a new approach for controlling the traffic at isolated intersections. We assume that all vehicles are equipped with on-board units (ITS station) that make them able to wirelessly negotiate the "right of way" according to the measurements done by the positioning system during their travel. A vehicle is allowed to cross the intersection if the green color is displayed to the driver in an on-board screen. The control aims to smooth the traffic through the sequence of vehicles authorized to traverse the intersection. The main challenge raised with the assumption is that the sequence must be dynamically formed by a realtime application. The dynamic behavior of the traffic is considered discrete, in order to determine the switching rule according to the instantly observed events. We propose a model based on timed Petri Nets with Multipliers (TPNM) which allows us to propose the control policy through the structural analysis. The resulting switching rules are very simplistic and efficient for isolated intersections. Indeed, microscopic simulations show that they perform as well as the optimal sequence based on the detection of vehicles at the entrance of the intersection. Moreover, the proposed approach has been tested through a real intersection. (C) 2012 Elsevier Ltd. All rights reserved.
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