利用CGI增加WWW的交互性

该文首先讨论了ＣＧＩ及其与ＨＴＴＰ的关系，然后介绍了ＣＧＩ结合ＨＴＭＬ提供ＷＷＷ交互性的方法，最后给出了利用ＣＧＩ设计并实现一个基于ＷＷＷ的公告板系统。     

Measuring and modelling the performance of a parallel ODMG compliant object database server

Object database management systems (ODBMSs) are now established as the database management technology of choice for a range of challenging data intensive applications. Furthermore, the applications associated with object databases typically have stringent performance requirements, and some are associated with very large data sets. An important feature for the performance of object databases is the speed at which relationships can be explored. In queries, this depends on the effectiveness of different join algorithms into which queries that follow relationships can be compiled. This paper presents a performance evaluation of the Polar parallel object database system, focusing in particular on the performance of parallel join algorithms. Polar is a parallel, shared‐nothing implementation of the Object Database Management Group (ODMG) standard for object databases. The paper presents an empirical evaluation of queries expressed in the ODMG Query Language (OQL), as well as a cost model for the parallel algebra that is used to evaluate OQL queries. The cost model is validated against the empirical results for a collection of queries using four different join algorithms, one that is value based and three that are pointer based. Copyright © 2005 John Wiley & Sons, Ltd.     

Improving database performance with a mixed fragmentation design

The performance of database operations can be enhanced with an efficient storage structure design using attribute partitioning and/or tuple clustering. Previous research deals mostly with attribute partitioning. We address here the combined problem of attribute partitioning and tuple clustering. We propose a novel approach for this mixed fragmentation problem by applying a genetic algorithm iteratively to attribute partitioning and tuple clustering sub-problems. We compared our results to attribute-only partitioning and random search solution, resulting in a database access cost reduction of upto 70% and 67% respectively. We analyzed the effect of varying genetic parameters on the optimal solution through experimentation.     

Improving network systems performance by clustering distributed database sites

Clustering network sites is a vital issue in parallel and distributed database systems DDBS. Grouping distributed database network sites into clusters is considered an efficient way to minimize the communication time required for query processing. However, clustering network sites is still an open research problem since its optimal solution is NP-complete. The main contribution in this field is to find a near optimal solution that groups distributed database network sites into disjoint clusters in order to minimize the communication time required for data allocation. Grouping a large number of network sites into a small number of clusters effectively increases the transaction response time, results in better data distribution, and improves the distributed database system performance. We present a novel algorithm for clustering distributed database network sites based on the communication time as database query processing is time dependent. Extensive experimental tests and simulations are conducted on this clustering algorithm. The experimental and simulation results show that a better network distribution is achieved with significant network servers load balance and network delay, a minor communication time between network sites is realized, and a higher distributed database system performance is recognized.     

Improving hybrid ad hoc networks: The election of gateways

The selection of an appropriate and stable route that enables suitable load balancing of Internet gateways is an important issue in hybrid mobile ad hoc networks. The variables employed to perform routing must ensure that no harm is caused that might degrade other network performance metrics such as delay and packet loss. Moreover, the effect of such routing must remain affordable, such as low losses or extra signaling messages. This paper proposes a new method, Steady Load Balancing Gateway Election, based on a fuzzy logic system to achieve this objective. The fuzzy system infers a new routing metric named cost that considers several networks performance variables to select the best gateway. To solve the problem of defining the fuzzy sets, they are optimized by a genetic algorithm whose fitness function also employs fuzzy logic and is designed with four network performance metrics. The promising results confirm that ad hoc networks are characterized by great uncertainty, so that the use of Computational Intelligence methods such as fuzzy logic or genetic algorithms is highly recommended.     

Object versioning in an ODMG‐compliant object database system

In this paper, we describe the design and implementation of the SOP Object Version System which is built upon an object database system, called SOP (SNU ODBMS Platform). SOP is fully compliant with ODMG‐93, a standard for object databases proposed by the Object Database Management Group (ODMG). To support object versioning in an ODMG C++ OML (Object Manipulation Language) environment, the SOP Object Version System provides a set of APIs (Application Programming Interfaces) as a class library. One important design goal of the SOP Object Version System was to achieve full compliance with ODMG‐93 standard. That is, in designing the class library, we tried to utilize the ODMG‐93 C++ OML interface as much as possible, while preserving its semantics as defined in ODMG‐93. Our object version model follows the basic functionalities of mainstream object version models. Although this approach burdens programmers with the management of the application‐specific version policy, it helps users to apply the SOP Object Version System to diverse application areas. Copyright © 1999 John Wiley & Sons, Ltd.     

Contact sensing and grasping performance of compliant hands

Limitations in modern sensing technologies result in large errors in sensed target object geometry and location in unstructured environments. As a result, positioning a robotic end-effector includes inherent error that will often lead to unsuccessful grasps. In previous work, we demonstrated that optimized configuration, compliance, viscosity, and adaptability in the mechanical structure of a robot hand facilitates reliable grasping in unstructured environments, even with purely feedforward control of the hand. In this paper we describe the addition of a simple contact sensor to the fingerpads of the SDM Hand (Shape Deposition Manufactured Hand), which, along with a basic control algorithm, significantly expands the grasp space of the hand and reduces contact forces during the acquisition phase of the grasp. The combination of the passive mechanics of the SDM Hand along with this basic sensor suite enables positioning errors of over 5 cm in any direction. In the context of mobile manipulation, the performance demonstrated here may reduce the need for much of the complex array of sensing currently utilized on mobile platforms, greatly increase reliability, and speed task execution, which can often be prohibitively slow.     

Conformance specification in the CGI

The Computer Graphics Interface (CGI) is a developing International Organization for Standardization (ISO) standard proposal¹ that addresses the interface between a virtual graphics device and an implementation of one of the ISO functional standards (namely, Programmer's Hierarchical Interactive Graphics System (PHIGS)², Graphical Kernel System (GKS)³, and Graphical Kernel System for Three Dimensions (GKS-3D)⁴. This paper may interest those who are tracking the development of the CGI and describes a recently introduced method for structuring conformance to provide for a wide diversity of device technology and architecture, while also providing for the spread of functional specification requirements. This scheme involves the definition of a number of standard constituency profiles, and pays particular attention to the needs of GKS and the Computer Graphics Metafile (CGM)⁵ in accessing the virtual device through the CGI. It must be stressed that the CGI is an emerging standard, and has not yet achieved a state of technical stability.     

Scaling database performance on GPUs

The market leaders of Cloud Computing try to leverage the parallel-processing capability of GPUs to provide more economic services than traditions. As the cornerstone of enterprise applications, database systems are of the highest priority to be improved for the performance and design complexity reduction. It is the purpose of this paper to design an in-memory database, called CUDADB, to scale up the performance of the database system on GPU with CUDA. The details of implementation and algorithms are presented, and the experiences of GPU-enabled CUDA database operations are also shared in this paper. For performance evaluation purposes, SQLite is used as the comparison target. From the experimental results, CUDADB performs better than SQLite for most test cases. And, surprisingly, the CUDADB performance is independent from the number of data records in a query result set. The CUDADB performance is a static proportion of the total number of data records in the target table. Finally, this paper comes out a concept of turning point that represents the difference ratio between CUDADB and SQLite.     

NoSQL real-time database performance comparison

The amount of data being produced is increasing constantly, as the number and variety of connected devices are growing and the advances in data storage and mining are supporting this evolution. However, storing and handling high quantities of data is challenging the current Relational Database Management Systems. Big Data and its related products came to help in this matter, and the NoSQL databases arise with the purpose to offer better solutions and features to handle massive amounts of data with higher performance, sometimes near real-time. The present study presents the NoSQL databases scenario and background, and elaborates a detailed study with the characteristics, a features comparison and a performance evaluation of three different NoSQL databases extensively used in the market nowadays: Couchbase, MongoDB and RethinkDB. Tests were performed in two different scenarios: single thread and multiple threads. The results reveal that Couchbase had a better performance at most of the operations, except for retrieving multiple documents and inserting documents with multiple threads, operations in which MongoDB scored better.     

Improving the performance of kurtosis estimator

In this communication, sample measures of kurtosis adapted by various software packages are compared for data from normal and non-normal populations. Further, two improved estimators of population kurtosis are proposed and their performance is compared with the currently used measures. The suggested estimators have considerably lower mean squared error (MSE) for various sampling designs in our simulation study. Two empirical examples are given to illustrate the usefulness of suggested estimators in practice.     

Improving the performance of reverse debugging

Reverse debugging is the software development technique that effectively helps fix bugs occurring at the nondeterministic program behavior. It allows one to examine the past states of the program without rerunning it. An implementation of reverse debugging based on deterministic replay in the QEMU 2.0 emulator is described. A number of techniques improving the debugging performance due to reducing the amount of saved data, optimized storage of system snapshots, indexing, and compressing of the event log are proposed. The emulator can work together with the interactive GDB debugger, which makes it possible to use the reverse-continue, reverse-nexti, reverse-stepi and reverse-finish commands in the course of debugging. The execution time of these commands depends on the frequency of recording the system’s state snapshots. An estimate of the optimal frequency for the reverse-continue command is obtained.     

关系数据库性能优化研究

效率是数据库开发中经常遇到的问题，数据库性能的优劣将直接关系到软件的运行效率。为了提高数据库产品的性能，对影响关系数据库性能的一些主要因素进行了阐述。结合实际给出了数据库性能优化的一些建议并用实验数据证明之。分析和比较了不同设计方案可能对数据库性能的影响，提出了目前关于数据库性能优化的问题是没有通用方案的观点。     

嵌入式Linux系统CGI程序设计技术

在详细介绍一种嵌入式Web服务器BOA的实现与配置方法的基础上,以一个Web在线远程监控GPIO(通用输入/输出)的程序为实例,介绍嵌入式Linux系统下CGI程序设计技术。     

CGI training for the entertainment film industry

As the digital film industry matures, the education needed to become part of it also evolves and shifts. We must therefore rethink how we educate future digital entertainment workers. Barely three decades old, the computer graphics field has been through enormous changes. Possibilities and experimentation have evolved into commonly used and widely accepted tools to create effects, images, and characters for films. The education needed to succeed in the digital entertainment industry has also changed. The early emphasis on technical skills, especially computer science, has broadened to include a strong focus on art and animation skills. The reasons for this necessitate looking at the industry and education over the last twenty or so years (1975-98). While the article primarily addresses the entertainment film industry, that industry offered few digital production jobs before 1992. We must therefore consider the role that television commercials (and those ubiquitous “flying logos”) played in the development and adoption of digital technology in the film industry. In addition to theatrical motion pictures, the fast growing digital film industry now produces a wide variety of film based entertainment, from ride simulators to large format special venue theaters such as OmniMax and Imax     

数据库系统性能模型建模方法综述

数据库系统性能模型是数据库系统管理的重要基础技术支撑,广泛用于查询调度、资源分配、性能调优等任务中。当前的性能模型主要分为分析型和统计型两种,分析型模型需要深入研究数据库系统查询执行过程,对动态查询的适应性较好,无须成本高昂的采样实验,但在查询并行执行情景下建模复杂,对不同的数据库系统有不同的理论模型。统计型模型无须分析查询执行过程,通过采集查询执行参数并训练某个数学模型。统计型建模过程简单,能够较好地描述查询交互,预测效果较好,但采样成本很高,对动态查询的适应性差。对数据库系统性能建模的主要文献进行综述,重点介绍数据库系统性能建模的主要方法,并讨论这两类模型各自的优缺点、建模的难点以及应对策略。在此基础上,对数据库系统性能模型领域的研究做了展望,为有关该领域的研究提供参考。     

数据库性能预测的研究与应用

数据库性能预测具有可利用历史数据较少、受外界不确定性因素影响较大的特点.传统的构建数据库方法有采集数据周期长、普通人较难准确掌握、预测值波动性大等问题.为此探讨了一种应用数学公式,只需采集较少数据即可方便快速地预测数据库性能.使用该方法可以在数据库处于正常工作情况下,对今后一段时期内数据库性能做出较为快速准确的预测,有效预防未来可能出现的性能问题.     

Simulated performance of a data-driven database machine

One of the main limitations to high parallelism in database processing is the available 1/O bandwidth of the storage devices comprising the machine. One way to increase this bandwidth is to use multiple parallel disk units. The main problem with this approach is the lack of a computational model capable of utilizing any significant number of such devices. In this paper we present a different model, referred to as the Active Graph Model, which is based on the principles of asynchronous data-driven computation. To demonstrate the viability of this approach, we have implemented the model on a simulated multiprocessor architecture. By varying the speed of processors, memory units, communication links, and the types of queries processed, we demonstrate that the resulting database machine is capable of exploiting the I/O bandwidth of a large number of disk units as well as the computational power of the associated processors.