Query Translation on the Fly in Deep Web Integration

To facilitate users to access the desired information, many researches have dedicated to the Deep Web （i.e. Web databases） integration. We focus on query translation which is an important part of the Deep Web integration. Our aim is to construct automatically a set of constraints mapping rules so that the system can translate the query from the integrated interface to the Web database interfaces based on them. We construct a concept hierarchy for the attributes of the query interfaces, especially, store the synonyms and the types （e.g. Number, Text, etc.） for every concept At the same time, we construct the data hierarchies for some concepts if necessary. Then we present an algorithm to generate the constraint mapping rules based on these hierarchies. The approach is suitable for the scalability of such application and can be extended easily from one domain to another for its domain independent feature. The results of experiment show its effectiveness and efficiency.     

A Cache Considering Role-Based Access Control and Trust in Privilege Management Infrastructure

PMI （privilege management infrastructure） is used to perform access control to resource in an E-commerce or E-government system. With the ever-increasing need for secure transaction, the need for systems that offer a wide variety of QoS （quality-of-service） features is also growing. In order to improve the QoS of PMI system, a cache based on RBAC （Role-based Access control） and trust is proposed. Our system is realized based on Web service. How to design the cache based on RBAC and trust in the access control model is deseribed in detail. The algorithm to query role permission in cache and to add records in cache is dealt with. The policy to update cache is introduced also.     

The Configuration Strategies on Caching for Web Servers

The Web cluster has been a popular solution of network server system because of its scalability and cost effective ness. The cache configured in servers can result in increasing significantly performance, In this paper, we discuss the suitable configuration strategies for caching dynamic content by our experimental results. Considering the system itself can provide support for caching static Web page, such as computer memory cache and disk＇s own cache, we adopt a special pattern that only caches dynamic Web page in some experiments to enlarge cache space. The paper is introduced three different replacement algorithms in our cache proxy module to test the practical effects of caching dynamic pages under different conditions. The paper is chiefly analyzed the influences of generated time and accessed frequency on caching dynamic Web pages. The paper is also provided the detailed experiment results and main conclusions in the paper.     

Multi-Level Web Cache Model Used in Data Grid Application

This paper proposed a novel multilevel data cache model by Web cache （MDWC） based on network cost in data grid. By constructing a communicating tree of grid sites based on network cost and using a single leader for each data segment within each region, the MDWC makes the most use of the Web cache of other sites whose bandwidth is as broad as covering the job executing site. The experiment result indicates that the MDWC reduces data response time and data update cost by avoiding network congestions while designing on the parameters concluded by the environment of application.     

Extracting Result Schema Based on Query Instances in the Deep Web

Deep Web sources contain a large of high-quality and query-related structured date. One of the challenges in the Deep Web is extracting result schemas of Deep Web sources. To address this challenge, this paper describes a novel approach that extracts both result data and the result schema of a Web database. The approach first models the query interface of a Deep Web source and fills in it with a specifically query instance. Then the result pages of the Deep Web sources are formatted in the tree structure to retrieve subtrees that contain elements of the query instance, Next, result schema of the Deep Web source is extracted by matching the subtree＇ nodes with the query instance, in which, a two-phase schema extraction method is adopted for obtaining more accurate result schema. Finally, experiments on real Deep Web sources show the utility of our approach, which provides a high precision and recall.     

Semantic Cache Replacement Strategy for XML Algebra-Based Query Optimization

Aiming at the fact that traditional cache replacement strategy lacks pertinence to the semantic cache in the process of extensible markup language(XML) algebra query, a replacement strategy based on the semantic cache contribution value is proposed. First, pattern matching rules for XML algebra query and semantic caches are given. Second, the method of calculating the semantic cache contribution value is proposed. In XML documents with four different sizes, the experimental results of time efficiency show that this strategy supports environment of the XML algebra query and it has better time efficiency than both least frequency used(LFU) and least recently used(LRU).     

Design and Implementation of Hierarchy Cache Using Pagefile

This paper presents a novel hierarchy cache architecture for the purpose of optimizing IO performance. The main idea of the hierarchy cache is to use a few megabytes of RAM and a pagefile to form a two-level cache architecture. The pagefile is equivalent to the cache disk in DCD(Disk Caching Disk). The pagefile outperforms data disks, because data are accessed in different units and different ways. Small writes are collected in the RAM cache first, and data will be transferred to the pagefile in large writes later. When the system is idle, it will destage data from the pagefile to data disks. The performance test results show that the hierarchy cache can improve IO performance dramatically for small writes, and the mail server using the hierarchy cache driver can handle transactions about 2.2 times faster than the normal mail server. The hierarchy cache is implemented as a filter driver, so it‘s transparent to the current Windows 2000/Windows XP operating system.     

分类Cache库在Web查询系统中的应用

利用分类Cache库技术可以解决对已检索到的Web信息的再利用问题,通过使用分类Cache库,不但可以减少重复检索Web的次数,提高查询系统的效率,而且还可以对已检索到的Web信息实现基于语义的精确查询,提高系统的查询精确度.重点介绍了Web查询系统中分类Cache库的构造、管理与维护.     

公路网移动终端的KNN查询技术

公路网中移动兴趣点(POIs)的查询处理是一个难点,目前的研究多基于欧氏距离对静态POIs进行处理,不能很好地适应移动环境下终端弱连接和频繁移动的需要.文中在公路网移动计算场景下,设计了一种存储分区数据对象的结构来表示公路网图形模型,提出适用于移动终端的连续KNN查询(CQ-KNN)算法.该算法改进了Wang等提出的MKNN算法,将逐层渐近探测和检索边列表结合起来进行近邻查询,避免了MKNN算法在限定层数不够却不得不执行范围查询时所带来的开销;同时使用缓存策略来支持移动终端提交的连续查询请求,并给出基于广播位置失效报告的缓存一致性维护策略.仿真结果表明,CQ-KNN算法较MKNN算法有更快的CPU处理速度和更短的网络响应延时,并且能支持移动终端的离线KNN近似查询.     

活动缓存模式在知识管理系统中的应用

动态文档正在成为Web内容中越来越重要的组成部分,获取动态内容的缓存成为影响Web规模的重要课题.笔者提倡用“活动缓存模式”来支持动态内容在Web代理上的缓存.这种模式允许服务器提供“缓存小应用”,这些小应用与内容绑定,需要代理根据缓存命令中判定的结果调用缓存小应用来完成必要的处理,而不需要与服务器联系.说明活动缓存模式涉及的协议、接口和安全机制,阐述了在当前的知识管理系统中如何引入活动缓存机制,以此来解决在应用规模不断扩大和数据量不断增加的情况下知识管理系统服务器服务性能问题.     

A processing approach for event-based location aware queries in hybrid wireless sensor networks

In hybrid wireless sensor networks, sensor mobility causes the query areas to change dynamically. Aiming at the problem of inefficiency in processing the data aggregation queries in dynamic query areas, this paper proposes a processing approach for event-based location aware queries (ELAQ), which includes query dissemination algorithm, maximum distance projection proxy selection algorithm, in-network query propagation, and aggregation algorithm. ELAQs are triggered by the events and the query results are dependent on mobile sensors’ location, which are the characteristics of ELAQ model. The results show that compared with the TinyDB query processing approach, ELAQ processing approach increases the accuracy of the query result and decreases the query response time. Biography: HONG Liang (1982–), male, Ph.D. candidate, research direction: database system, sensor network.     

Design and implementation of a dynamic content cache module for Web server

Web offers a very convenient way to access remote information resources, an important measurement of evaluating Web services quality is how long it takes to search and get information. By caching the Web server‘s dynamic content, it can avoid repeated queries for database and reduce the access frequency of original resources, thus to improve the speed of server‘s response. This paper describes the concept. advantages, principles and concrete realization procedure of a dvnamic content cache module for Web server.     

QJoin：质量驱动的乱序数据流连接处理技术

数据流乱序现象会导致数据流处理结果的丢失,给数据流的分析处理带来了巨大困难。本研究探讨了质量驱动下的乱序数据流连接处理问题,提出一种质量驱动的乱序数据流连接处理技术(QJoin)。QJoin采用缓冲存储技术和对称连接策略,实现并确保对流元组进行即时分析处理,从而降低了流元组处理的平均等待时间。同时,基于质量驱动的理念,根据临近阶段连接处理过程中收集统计的数据,自适应地调整和优化内存缓存区的大小,从而在满足用户结果质量要求的前提下,降低系统内部历史数据的内存缓存量,尽可能保证迟到元组的连接处理完整性。真实数据集上的实验结果表明,与传统的数据流乱序处理技术MP-K-slack相比,QJoin在满足用户结果质量要求的前提下,确保能够即时地分析处理数据流的流元组,显著降低系统的内存开销。     

一种物化Web视图的在线选择算法

建立了一个考虑更新代价的Web视图置换测度模型,并以此为基础,提出一种物化Web视图在线选择算法DCR.该算法在简单的缓存算法基础上引入了选择置换机制, 通过监测提交的用户查询, 决定是否将其结果予以保存, 必要时依据置换测度值的大小进行置换, 实现Web视图物化总量的控制, 防止视图过分物化, 以降低动态缓存管理、索引和检索的开销.同时可结合适当的维护方式, 提高更新效率, 避免频繁的更新对查询性能产生太大的影响, 使整个算法更具适用性. 实验表明, 在查询集较大、数据源更新比较频繁的场合, DCR算法可以降低视图检索开销, 并可通过机会更新有效减少了失效视图的数量,使算法在用户查询响应性能方面显示出较大的优势.     

Cache Coherency Design in Pentium Ⅲ SMP System

This paper analyzes cache coherency mechanism from the view of system. It firstly discusses caehe-memory hierarchy of Pentium Ⅲ SMP system, including memory area distribution, cache attributes control and bus transaction. Secondly it analyzes hardware snoopy mechanism of P6 bus and MESI state transitions adopted by Pentium Ⅲ. Based on these, it focuses on how muhiprocessors and the P6 bus cooperate to ensure cache coherency of the whole system, and gives the key of cache coherency design.