Efficient methods for finding an optimal network location for travel planning

The Journal of Supercomputing - In this paper, we describe an optimal network location for travel planning (ONLTP) query, a type of optimal location query. In trip planning, finding the optimal...     

Some approaches for processing SQLf nested queries

This article deals with query processing techniques for the SQLf language which is an extended version of SQL supporting imprecise queries interpreted in the framework of fuzzy sets. SQLf, as well as SQL, allows for the use of nested queries, in which a (fuzzy) condition involved in a select block, calls on another select block (the nested one). Two types of processing strategies for nested queries are discussed. The first one tends to take advantage of existing database management systems (DBMS) to process fuzzy queries thanks to an additional layer which is in charge of translating the initial query into a Boolean one. In this perspective, the performances obtained depend strongly on the efficiency of the underlying DBMS. The other strategy is slightly different and it is situated in the context of the design of systems involving specific algorithms for processing fuzzy queries. In this article, the focus is put on algorithms related to the generic nesting construct “exists.” © 1996 John Wiley & Sons, Inc.     

A comparative study of Minimax Probability Machine-based approaches for face recognition

Automatic face recognition is a challenging problem in the biometric recognition area. Minimax Probability Machine (MPM) and its extension, Minimum Error Minimax Probability Machine, have shown advantages in the machine learning literature. In this paper, we incorporate the MPM-based approaches into our face recognition system for further study. To test the performance of our new system, we compare the MPM-based approaches with SVM, a PCA-based and a LDA-based algorithms on the FERET database for both verification and identification. The experimental results demonstrate that MPM-based approaches are promising for automatic face recognition.     

A comparative study of network robustness measures

The robustness is an important functionality of networks because it manifests the ability of networks to resist failures or attacks. Many robustness measures have been proposed from different aspects, which provide us various ways to evaluate the network robustness. However, whether these measures can properly evaluate the network robustness and which aspects of network robustness these measures can evaluate are still open questions. Therefore, in this paper, a thorough introduction over attacks and robustness measures is first given, and then nine widely used robustness measures are comparatively studied. To validate whether a robustness measure can evaluate the network robustness properly, the sensitivity of robustness measures is first studied on both initial and optimized networks. Then, the performance of robustness measures in guiding the optimization process is studied, where both the optimization process and the obtained optimized networks are studied. The experimental results show that, first, the robustness measures are more sensitive to the changes in initial networks than to those in optimized networks; second, an optimized network may not be useful in practical situations because some useful functionalities, such as the shortest path length and communication efficiency, are sacrificed too much to improve the robustness; third, the robustness of networks in terms of closely correlated robustness measures can often be improved together. These results indicate that it is not wise to just apply the optimized networks obtained by optimizing over one certain robustness measure into practical situations. Practical requirements should be considered, and optimizing over two or more Received February 22, 2016; accepted September 29, 2016 E-mail: neouma@163.com suitable robustnessmeasures simultaneously is also a promising way.     

网络存储方案的比较研究

本论文对存储技术做了相应的介绍、分析和比较,NAS系统主要负责提供文件共享,在网络日益复杂的演化中,系统的可维护性也是一个极其重要的考虑因素。随着网络的功能逐渐完善,相应地对存储系统的性能要求也就逐渐提高,就需要NAS（Network Attached Storage）或SAN（Storage Area Network）技术。在一个网络中安装了NAS设备后,系统可以有明显的性能方面的提高和管理成本的降低。     

An efficient method for privacy preserving location queries

Recently, the issue of privacy preserving location queries has attracted much research. However, there are few works focusing on the tradeoff between location privacy preservation and location query information collection. To tackle this kind of tradeoff, we propose the privacy persevering location query (PLQ), an efficient privacy preserving location query processing framework. This framework can enable the location-based query without revealing user location information. The framework can also facilitate location-based service providers to collect some information about the location based query, which is useful in practice. PLQ consists of three key components, namely, the location anonymizer at the client side, the privacy query processor at the server side, and an additional trusted third party connecting the client and server. The location anonymizer blurs the user location into a cloaked area based on a map-hierarchy. The map-hierarchy contains accurate regions that are partitioned according to real landforms. The privacy query processor deals with the requested nearest-neighbor (NN) location based query. A new convex hull of polygon (CHP) algorithm is proposed for nearest-neighbor queries using a polygon cloaked area. The experimental results show that our algorithms can efficiently process location based queries.     

BitTorrent-like P2P approaches for VoD: A comparative study

The enormous popularity of Video on Demand (VoD) has attracted substantial research attention into the effective use of peer-to-peer (P2P) architectures to provide solutions at large-scale. In particular, the high efficiency of BitTorrent has inspired many P2P protocols for VoD. However, these protocols use different approaches to adapt the design of Bittorrent to VoD, and in most cases their performance has been evaluated separately and in limited scenarios. As a consequence, the research community still lacks a clear understanding of how these protocols compare against each other and how well each of them would work in real world conditions, where, for instance, peers have heterogeneous bandwidths, may freeride or may be located behind NAT/firewall.In this paper, we propose a simulation based methodology which aims at putting forward a common base for comparing the performance of these different protocols under a wide range of conditions. We show that, despite their considerable differences: (i) existing BitTorrent-like VoD approaches all share some characteristics, such as that their bandwidth reciprocity based methods to incentivize cooperation do not always yield an optimal overall performance. Furthermore, we demonstrate that (ii) in these protocols there is a trade-off between QoS and resilience to freeriding and malicious attacks. We also discover that, (iii) when peers doing streaming coexist with peers doing traditional file transfer, the latter actually benefit from this coexistence, at the expenses of the former. Finally, we show that (iv) early departures of peers from the system do not significantly affect the QoS delivered, while jumping to a different position in the file has a bigger negative impact. Overall, our findings provide important implications for both VoD service providers and future system designers. On the one hand, our results can guide VoD service providers in selecting the most appropriate protocol for a given environment. On the other hand, exposing the flaws of current approaches will help researchers in improving them and/or designing better ones.     

A comparative study of two shovel designs

In the present study a modified shovel design with two perpendicular shafts is presented. This modified, two-shaft shovel was compared with a regular shovel. The modified shovel was evaluated and tested in a controlled laboratory environment using surface electromyography recorded from the lumbar paraspinal muscles. The new shovel design was also tested in a field study using ratings of perceived exertion. The results indicate that there was a significant reduction in EMG values of the lumbar paraspinal muscles and a consistent reduction in perceived exertion ratings while the modified shovel was being used for removing dirt in digging trenches up to 90 cm in depth.     

Correction to: Efficient methods for finding an optimal network location for travel planning

The Journal of Supercomputing - A correction to this paper has been published: https://doi.org/10.1007/s11227-021-03837-x     

A spatial model for complex objects with a broad boundary supporting queries on uncertain data

This paper proposes a new data model for spatial databases that supports spatial entities with a broad boundary. The model is proposed as a solution to the problem of handling uncertainty in spatial data. Broad boundaries absorb all the uncertainty by which spatial data are commonly affected and allow computations in presence of uncertainty without rough simplifications of the reality. A specific model for topological relations between regions with a broad boundary is then developed and hierarchically structured topological operators are proposed. Such operators allow users to progressively refine their queries and constitute the basis for a spatial extension to SQL. The model proposed in the paper can be easily integrated into existing data models for spatial databases.     

对位置信息服务的连续查询攻击算法

为了解决连续查询攻击算法给位置信息服务(LBS)带来的安全隐患,基于已有的k-匿名化Cloaking算法提出了一种新的连续查询攻击算法--CQACA。该算法首先利用熵和查询匿名度量定义了查询识别率的目标函数,并结合元胞蚁群给出了目标函数的求解算法。最后,利用移动对象数据生成器进行实验,深入研究了影响CQACA的关键因素,同时对比分析了该算法与Cloaking算法的性能差异:CQACA与实际数据的误差为13.27%,而Cloaking算法则为17.35%。结果表明CQACA具有一定的有效性。     

A comparative study of delayed stroke handling approaches in online handwriting

International Journal on Document Analysis and Recognition (IJDAR) - Delayed strokes, such as i-dots and t-crosses, cause a challenge in online handwriting recognition by introducing an extra...     

Distributed evaluation of network directory queries

We describe novel efficient techniques for the distributed evaluation of hierarchical aggregate selection queries over LDAP directory data, distributed across multiple autonomous directory servers. Such queries are useful for emerging applications like the directory enabled networks initiative. Our techniques follow the LDAP approach of distributed query evaluation by referrals, where each relevant server computes answers locally, and the LDAP client coordinates between directory servers. We make a conceptual separation between the identification of relevant servers and the distributed computation of answers. We focus on the challenging task of generating an efficient plan for evaluating hierarchical aggregate selection queries, which involves correlating directory entries across multiple servers. The key features of our plan are: 1) the network traffic consists of query answers, and auxiliary messages that depend only on the number of servers and the size of the query (not on the data size), 2) the coordination effort at the client is independent of the data size, and 3) potentially expensive server-to-server communication and coordination is avoided. We complement our analysis with experiments that show the robustness and scalability of our techniques for highly distributed directory query processing.     

QoS-aware optimization of sensor network queries

The resource-constrained nature of mote-level wireless sensor networks (WSNs) poses challenges for the design of a general-purpose sensor network query processors (SNQPs). Existing SNQPs tend to generate query execution plans (QEPs) that are selected on the basis of a fixed, implicit expectation, for example, that energy consumption should be kept as small as possible. However, in WSN applications, the same query may be subject to several, possibly conflicting, quality-of-service (QoS) expectations concomitantly (for example maximizing data acquisition rates subject to keeping energy consumption low). It is also not uncommon for the QoS expectations to change over the lifetime of a deployment (for example from low to high data acquisition rates). This paper describes optimization algorithms that respond to stated QoS expectations (about acquisition rate, delivery time, energy consumption and lifetime) when making routing, placement, and timing decisions for in-WSN query processing. The paper shows experimentally that QoS-awareness offers significant benefits in responding to, and reconciling, diverse QoS expectations, thereby enabling QoS-aware SNQPs to generate efficient QEPs for a broader range WSN applications than has hitherto been possible.     

A comparative study of tests for the difference of two Poisson means

We investigate different test procedures for testing the difference of two Poisson means. Asymptotic tests, tests based on an approximate p-value method, and a likelihood ratio test are considered. Size and power performance of these tests are studied by means of Monte Carlo simulation under different settings. If one wants to control the actual significance level at or below the pre-chosen nominal level, tests based on approximate p-value method are the desirable candidates. If one allows tests whose actual significance levels may occasionally exceed the pre-chosen nominal level by an acceptable margin, asymptotic tests based on an unbiased estimate and constrained maximum likelihood estimate are reasonable alternatives. We illustrate these testing procedures with a breast cancer example.     

Some properties of optimal cartesian product files for orthogonal range queries

Cartesian product file (CPF) has been proposed as a good multi-attribute file structure. Although designing an optimal CPF for partial match queries (PMQs) has been proven to be NP-hard, some useful properties have been studied for PMQs to help the work. However, a good CPF for PMQs may not be beneficial for orthogonal range queries (ORQs). Therefore, in this paper, we intend to study properties that help the design of a good CPF for ORQs. We found that the problem of designing the optimal CPF for ORQs is related to the problem of finding a minimal-f N-tuple. We will also show some theories of minimal-f N-tuples and develop a method for generating a minimal-f N-tuple. Finally, we will present some properties of the optimal CPF for ORQs from the theories of minimal-f N-tuples.     

The optimal location of replicas in a network using a READ-ONE-WRITE-ALL policy

We consider the problem of locating replicas in a network to minimize communications costs. Under the assumption that the read-one-write-all policy is used to ensure data consistency, an optimization problem is formulated in which the cost function estimates the total communications costs. The paper concentrates on the study of the optimal communications cost as a function of the ratio between the frequency of the read and write operations. The problem is reformulated as a zero-one linear programming problem, and its connection to the p-median problem is explained. The general problem is proved to be NP-complete. For path graphs a dynamic programming algorithm for the problem is presented. Received: May 1993 / Accepted: June 2001