kHTTPd—内核级Web服务器代码分析（二）

kHTTPd是一个基于Linux内核特点的嵌入式服务器，因为这个服务器程序存在于内核之中，在从Linux往嵌入式方向移植的过程中可以不撤任何修改的移入，因此是一个性能较高、服务质量较好的网络服务器方案。本将分成三部分刊登，这里介绍服务器运行过程中调用的两个函数ManagementDaemon()、MainDsemon()。     

基于RTLinux的多通道实时网络系统设计

主要借鉴Linux/RK的资源调度思想，为嵌入式实时Linux提出了一种网络实时方案。主要对现有的RTLinux进行改造，突出网络实时的应用。通过改造Linux的网络子系统，得到一个微型网络子系统，移植到RTlinux微内核中。为网络子系统设计多个处理通道，支持网络并发调度，这由多个针对不同应用的内核线程实现。解决了Linux系统中网络实时性能不高的问题。     

Linux上IP over X.25的设计及其实现

针对Linux现有内核对IP网络广域网链路层协议支持上的不足之处，分析了现有IP over X.25的实现方案和局限性，结合作者参与研发的一款基于Linux的路由器的实践，提出并实现了一种在Linux内核级实现IP over X．25的新的实现方案，并在此基础上提出了一个在Linux中实现各种链路层协议上承载IP的通用软件框架。     

基于Linux的嵌入式系统在防火墙中的应用

本文提出了一种基于Linux的嵌入式系统的防火墙方案，文章首先分析了Linux作为嵌入式操作系统的优点，然后详细介绍了构造基于Linux的嵌入式系统防火墙的方案，包括确定硬件平台、选择合适的Linux发行版本、设计防火墙系统的硬件结构、防火墙系统软件的实现。     

VoIP网关中多链路SIP信令模块的设计与实现

文中在基于Linux操作系统的VoIP网关中，以单链路SIP信令实现为基础，提出了采用多进程架构的多链路SIP信令模块的设计实现方案。该设计继承了SIP协议固有的简单，可扩展性强等优点，而且多进程架构的设计结构清晰，能同时支持多路VoIP会话的建立与维护，解决了多用户的VoIP服务接入问题。该方案目前已用于基于Linux平台的VoIP网关的信令实现，完全满足VoIP网关的多链路处理与维护的需求。     

Linux下IPv6高级路由器的实现

介绍了IPv6的网络路由器的原理和在Linux上的具体实现方法。讨论了在Linux下如何组建IPv6网络试验平台,重点讨论如何将Linux工作站配置成路由器。然后介绍了静态路由和动态RIPng路由服务在Linux下的实现方法。     

基于Linux内核的实时调度机制研究及实现

分析了Linux操作系统内核提供的软实时调度机制及其存在的问题,阐述了基于Linux内核构建实时Linux操作系统的技术方案。着重介绍了RTLinux实时内核的结构框架,并对RTLinux的中断处理机制与调度机制进行了设计与实现。     

Linux可抢占内核的分析

Linux原有的内核是不可抢占的，这使得Linux不能很好地支持响应速度要求高的实时应用。利用Linux对SMP多处理器系统的支持，可以方便地将Linux内核改造为完全可抢占的。分析了Linux可抢占内核的实现原理，并对两种可抢占内核的实现方案作了比较。     

基于嵌入式Web的远程声级计测控系统

为了实现本地对远程声级计的测控,提出了基于嵌入式Linux操作系统并采用B/S(浏览器/服务器)架构实现嵌入式远程实时数据采集和控制的方案.该方案将Java Applet程序嵌入到静态网页中去,实现了远程声级计测控系统的数据动态Web显示.应用实践表明,该方案实现的远程声级计测控系统人机界面友好、使用简单、软件升级和维护方便快捷.     

Linux-i386平台可执行文件代码保护技术

针对Linux平台下软件保护技术的不足,对Linux可执行文件的代码保护进行了研究,并实现了一个运行于Linux-i386系统上的静态链接可执行文件保护程序LEP(Linux Executablc Protector)。     

嵌入式Linux下基于CGI的动态Web的实现

为在资源有限的嵌入式系统中有效地实现动态Web,文章提出了一种解决方案：在嵌入式Linux操作系统下,采用Boa作为wleb服务器,用C语言进行CGI程序设计,完成动态Web页面的实现。测试结果证明了该方案的正确性和有效性。     

关于国内可公开访问网页数量的一种估计

可公开访问网页是由Web上的静态网页和无需额外输入即可访问的动态网页两部分组成。基于CNNIC关于网络信息数量资源的调查报告与北大天网实际搜集所获得的数据,根据Web发展变化的数学模型,该文对过去和未来国内可公开访问网页的数量进行了一种估计。     

补充反馈模块的深度标注框架研究

由数据库生成的动态Web页是静态页面的数百倍,直接针对Web页产生过程的深度标注可以提高动态Web页的标注效率。针对动态Web页以查询生成居多的特点,提出标注与反馈相结合的深度标注框架,即第一步通过标注模块进行初步标注,并记录Web页面的查询要求;第二步分析查询信息,找出不同Web页的关系,通过反馈模块进一步补充标注内容,从而提高标注的质量。     

动态网页分发加速技术研究

随着Web技术的迅速发展,动态和个性化网页的比重日益增加,而传统缓存一般只适用于静态内容,难以减少获取动态网页所需的流量和延时代价。为了更有效地分发动态网页,人们提出了各种动态内容加速方案。文中研究了典型的动态网页分发加速方法,并对相关的加速技术进行了分析和比较。针对ESI和CDE这两种技术的优缺点,提出基于共享片段的动态网页分发加速模型。实验结果表明,与ESI和CDE相比,该模型可以节省更多的带宽,减少更多的延时。     

Deep Web structure

Our current understanding of Web structure is based on large graphs created by centralized crawlers and indexers. They obtain data almost exclusively from the so-called surface Web, which consists, loosely speaking, of interlinked HTML pages. The deep Web, by contrast, is information that is reachable over the Web, but that resides in databases; it is dynamically available in response to queries, not placed on static pages ahead of time. Recent estimates indicate that the deep Web has hundreds of times more data than the surface Web. The deep Web gives us reason to rethink much of the current doctrine of broad-based link analysis. Instead of looking up pages and finding links on them, Web crawlers would have to produce queries to generate relevant pages. Creating appropriate queries ahead of time is nontrivial without understanding the content of the queried sites. The deep Web's scale would also make it much harder to cache results than to merely index static pages. Whereas a static page presents its links for all to see, a deep Web site can decide whose queries to process and how well. It can, for example, authenticate the querying party before giving it any truly valuable information and links. It can build an understanding of the querying party's context in order to give proper responses, and it can engage in dialogues and negotiate for the information it reveals. The Web site can thus prevent its information from being used by unknown parties. What's more, the querying party can ensure that the information is meant for it.     

一种Deep Web爬虫的设计与实现

随着World Wide Web的快速发展,Deep Web中蕴含了越来越多的可供访问的信息.这些信息可以通过网页上的表单来获取,它们是由Deep Web后台数据库动态产生的.传统的Web爬虫仅能通过跟踪超链接检索普通的Surface Web页面,由于没有直接指向Deep Web页面的静态链接,所以当前大多数搜索引擎不能发现和索引这些页面.然而,与Surface Web相比,Deep Web中所包含的信息的质量更高,对我们更有价值.本文提出了一种利用HtmlUnit框架设计Deep Web爬虫的方法.它能够集成多个领域站点,通过分析查询表单从后台数据库中检索相关信息.实验结果表明此方法是有效的.     

一种提高Web响应性能的缓存机制

对于一个日访问量达到万级以上的网站来说,浏览速度将会成为该系统的一个瓶颈。如果能够优化内容发布系统,并把非实时更新的页面转换成静态页面,将会使浏览速度得到显著的提升。本文提出一种基于Java和XML技术、在MVC2架构基础上的三级缓存机制,从静态页面、组件到数据对象分别进行缓存,根据点击率来更新缓存,有效降低了多层体系结构之间的通信量,提高了Web的响应性能。     

基于GAA-API的Web网页细粒度访问控制方法研究

基于通用的授权与访问控制接口GAA-API，提出了一种网页的细粒度授权与访问控制方法。为网页中的静态资源元素、动态资源元素分别提供细粒度、灵活的访问控制。最后对该方法进行实验测试，并对测试结果进行比较分析。     

Special Issue in Honor of Ben Shneiderman's 60th Birthday: Reflections on Human-Computer Interaction

Abstract

Unlike most Web portals in the world, Chinese Web portals are characterized by a huge amount of information, excessive visual stimuli, and very long Web pages. The objective of this study is to investigate the effect of such rich Web portal designs and floating animations on visual search, emphasizing a comparison between Chinese users and German users. Two experiments were conducted to test 2 proposed hypotheses. Experiment 1 studied the effect of Web portal design (rich and simple) on visual search performance (performance time, errors, and satisfaction) with both Chinese and German participants. Experiment 2 studied the effects of static animations (leaderboards, couplets, and large squares) and floating animations (moving down, moving up/down, and random movement) on visual search performance on Web portals. The dependent variables were the performance time, error, satisfaction, and animation recognition. The results indicated that participants using simple Web portals searched faster, made fewer errors, and were more satisfied than participants using rich Web portals. No significant differences were found between the performance time of Chinese participants and German participants. However, satisfaction of Chinese participants was found to be less influenced by the differences between simple and rich Web portal designs, compared with German participants. No significant differences were found in performance time and animation recognition between static animations and floating animations, which indicated that users are able to detect the pattern of animation movements and were able to avoid floating animations as well as static animations. People searching pages with randomly floating animations were found to use significantly more time compared with those searching pages with no animations. Furthermore, users' satisfaction for pages with randomly floating animations, moving down animations, and moving up/down animations was significantly lower than for pages with no animations. Implications for designers and for future research are discussed.     

Databases deepen the Web

The Web has become the preferred medium for many database applications, such as e-commerce and digital libraries. These applications store information in huge databases that users access, query, and update through the Web. Database-driven Web sites have their own interfaces and access forms for creating HTML pages on the fly. Web database technologies define the way that these forms can connect to and retrieve data from database servers. The number of database-driven Web sites is increasing exponentially, and each site is creating pages dynamically-pages that are hard for traditional search engines to reach. Such search engines crawl and index static HTML pages; they do not send queries to Web databases. The information hidden inside Web databases is called the "deep Web" in contrast to the "surface Web" that traditional search engines access easily. We expect deep Web search engines and technologies to improve rapidly and to dramatically affect how the Web is used by providing easy access to many more information resources.