This paper presents the results of an empirical study aiming at comparing the support provided by ER and UML class diagrams during maintenance of data models. We performed one controlled experiment and two replication...
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This paper presents the results of an empirical study aiming at comparing the support provided by ER and UML class diagrams during maintenance of data models. We performed one controlled experiment and two replications that focused on comprehension activities (the first activity in the maintenance process) and another controlled experiment on modification activities related to the implementation of given change requests. The results achieved were analyzed at a fine-grained level aiming at comparing the support given by each single building block of the two notations. Such an analysis is used to identify weaknesses (i.e., building blocks not easy to comprehend) in a notation and/or can justify the need of preferring ER or UML for data modeling. The analysis revealed that the UML class diagrams generally provided a better support for both comprehension and modification activities performed on data models as compared to ER diagrams. Nevertheless, the former has some weaknesses related to three building blocks, i.e., multi-value attribute, composite attribute, and weak entity. These findings suggest that an extension of UML class diagrams should be considered to overcome these weaknesses and improve the support provided by UML class diagrams during maintenance of data models.
Cloud storage has become an important part of a cloud system nowadays. Most current cloud storage systems perform well for large files but they cannot manage small file storage appropriately. With the development of c...
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Cloud storage has become an important part of a cloud system nowadays. Most current cloud storage systems perform well for large files but they cannot manage small file storage appropriately. With the development of cloud services, more and more small files are emerging. Therefore, we propose an optimized data replication approach for small files in cloud storage systems. A small file merging algorithm and a block replica placement algorithm are involved in this approach. Small files are classified into four types according to their access frequencies. A number of small files will be merged into the same block based on which type they belong to. And the replica placement algorithm helps to improve the access efficiencies of small files in a cloud system. Related experiment results demonstrate that our proposed approach can effectively shorten the time spent reading and writing small files, and it performs better than the other two already known data replication algorithms: HAR and SequenceFile.
This paper describes an experimental investigation of adaptive control algorithms applied to aeroacoustic instabilities. The study is carried out on a cold how experimental rig, designed to reproduce the essential fea...
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This paper describes an experimental investigation of adaptive control algorithms applied to aeroacoustic instabilities. The study is carried out on a cold how experimental rig, designed to reproduce the essential features of acoustically coupled vortex shedding. This mechanism is the source of thrust oscillations in large segmented solid rocket motors. It is also found in a wide variety of combustion instabilities. Two adaptive control strategies are investigated and selected experimental results are reported. These results show the feasibility of control. The effect of the controller on the instability mechanism is analyzed and improvements to the control strategy are proposed. (C) 2000 Academic Press.
This article reviews routing algorithms in heterogeneous wireless networks with the goal of including QoS awareness. After a general overview of the issues and challenges of QoS provisioning over heterogeneous network...
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This article reviews routing algorithms in heterogeneous wireless networks with the goal of including QoS awareness. After a general overview of the issues and challenges of QoS provisioning over heterogeneous networks, classic routing strategies are revisited, and how they can be exploited to achieve QoS efficiency is discussed. In particular, for the considered scenarios our proposal is to account for some proactivity in the routing algorithms, as well as a QoS-driven control selection, which are shown to improve throughput, delay, and energy consumption. Finally, we introduce a general backward utility formulation for user satisfaction as a tool to capture complex and dynamic QoS variations.
For unsupervised color image segmentation, we propose a two-stage algorithm, KmsGC, that combines K-means clustering with graph cut. In the first stage, K-means clustering algorithm is applied to make an initial clust...
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For unsupervised color image segmentation, we propose a two-stage algorithm, KmsGC, that combines K-means clustering with graph cut. In the first stage, K-means clustering algorithm is applied to make an initial clustering, and the optimal number of clusters is automatically determined by a compactness criterion that is established to find clustering with maximum intercluster distance and minimum intracluster variance. In the second stage, a multiple terminal vertices weighted graph is constructed based on an energy function, and the image is segmented according to a minimum cost multiway cut. A large number of performance evaluations are carried out, and the experimental results indicate the proposed approach is effective compared to other existing image segmentation algorithms on the Berkeley image database.
In this paper we present a new iterative greedy algorithm for distributed compressed sensing (DCS) problem based on the backtracking technique, which can reconstruct several input signals simultaneously by processing ...
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In this paper we present a new iterative greedy algorithm for distributed compressed sensing (DCS) problem based on the backtracking technique, which can reconstruct several input signals simultaneously by processing column by column of the compressed signals, even when the measurements are contaminated with noise and without any prior information of their sparseness. This makes it a promising candidate for many practical applications when the number of non-zero (significant) coefficients of a signal is not available. Our algorithm can provide a fast runtime while also offers comparably theoretical guarantees as the best optimization-based approach in both the noiseless and noisy regime. Numerical experiments are performed to demonstrate the validity and high performance of the proposed algorithm. (C) 2011 Elsevier Ltd. All rights reserved.
We study the tractor and semi-trailer routing problem (TSRP), a variant of the vehicle routing problem (VRP). In the TSRP model for this paper, vehicles are dispatched on a trailer-flow network where there is only one...
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We study the tractor and semi-trailer routing problem (TSRP), a variant of the vehicle routing problem (VRP). In the TSRP model for this paper, vehicles are dispatched on a trailer-flow network where there is only one main depot, and all tractors originate and terminate in the main depot. Two types of decisions are involved: the number of tractors and the route of each tractor. Heuristic algorithms have seen widespread application to various extensions of the VRP. However, this approach has not been applied to the TSRP. We propose a heuristic algorithm to solve the TSRP. The proposed heuristic algorithm first constructs the initial route set by the limitation of a driver's on-duty time. The candidate routes in the initial set are then filtered by a two-phase approach. The computational study shows that our algorithm is feasible for the TSRP. Moreover, the algorithm takes relatively little time to obtain satisfactory solutions. The results suggest that our heuristic algorithm is competitive in solving the TSRP.
A method to transmit multiplexed digital video that potentially allows for video quality and capacity gains over conventional constant bit-rate (CBR) transmission is described. The method uses a joint rate control alg...
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A method to transmit multiplexed digital video that potentially allows for video quality and capacity gains over conventional constant bit-rate (CBR) transmission is described. The method uses a joint rate control algorithm that regulates the encoders during buffer congestion periods using bandwidth re-allocation and source rate control. A multichannel joint rate control algorithm is described and its performance simulated for MPEG encoded video on a typical Direct Broadcast Satellite (DBS) indicate significant capacity and/or quality gains conventional CBR transmission methods.
A novel approach is developed and demonstrated to characterize the sampling line effects during dynamic monitoring of fluid concentrations. The "sampling line" in this study refers to all components between ...
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A novel approach is developed and demonstrated to characterize the sampling line effects during dynamic monitoring of fluid concentrations. The "sampling line" in this study refers to all components between the point of fluid sampling and the point of analyzer sensor. In general, sampling lines introduce errors in measurements by altering the sample properties due to the fluid transport in the line as well as the adsorption and desorption of fluid constituents on the surfaces of the sampling components that come into contact with the sample fluid. A methodology based on a sampling line simulator is developed for taking these effects into account and correcting the measurements. The model is validated by direct experimental measurements using several different analyzers under various conditions. The sampling line simulator can be used to analyze the effect of various sampling configurations and operating conditions;this would be helpful in the design of sampling lines and their location. An algorithm is proposed that can be used to convert concentration values measured and reported by the analyzer to the concentration values at the point of sampling that are the actual and desired Values.
Thwarting severe cryptographic hardware attacks requires new approaches to logic and physical designs. This paper presents a systematic design approach to fault tolerant cryptographic hardware designs by combining the...
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Thwarting severe cryptographic hardware attacks requires new approaches to logic and physical designs. This paper presents a systematic design approach to fault tolerant cryptographic hardware designs by combining the concurrent error detection and correction, and uniform switching activity cells. The effectiveness of the Hamming code based error correction schemes as a fault tolerance method in stream ciphers is investigated. Coding is applied to Linear Feedback Shift Registers (LFSR) based stream cipher implementations. The method was implemented on industrial standard stream ciphers, e.g. A5/1(GSM), E0 (Bluetooth), RC4 (WEP), and W7. The performance of stream cipher algorithms with error detection and correction was studied by synthesising the designs on FPGA and custom Integrated Circuits. The hardware building blocks are investigated to minimise switching activity of a circuit for all possible inputs and their transitions by adding redundant gates and increasing the overall number of signal transitions. The overheads of the proposed approach are also discussed. (C) 2013 Elsevier Ltd. All rights reserved.
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