基于本体的网络数据工作平台NetData

近年来，网格、语义网络等新技术迅速发展并日臻成熟。互联网发展焦点开始从信息的发布和互联转向知识的交互框架。随着语义网络迅速发展，世界各地各个领域的研究爱好者组成虚拟社区，对同一领域的知识信息一起协作研究。其中，对数据的整理、保存、检索、分析是实现语义网络远景的基础工作。本文为了帮助研究社区的研究人员更有效方便地加入社区的研究，利用长期帮助中国中医研究院建设专业结构化数据库群的项目中所取得的经验，结合了语义网络和数据库网格的研究，设计并初步实现了基于本体的网络数据工作平台。     

Efficient data distribution in a Web server farm

High-performance Web sites rely on Web server `farms', hundreds of computers serving the same content, for scalability, reliability, and low-latency access to Internet content. Deploying these scalable farms typically requires the power of distributed or clustered file systems. Building Web server farms on file systems complements hierarchical proxy caching. Proxy caching replicates Web content throughout the Internet, thereby reducing latency from network delays and off-loading traffic from the primary servers. Web server farms scale resources at a single site, reducing latency from queuing delays. Both technologies are essential when building a high-performance infrastructure for content delivery. The authors present a cache consistency model and locking protocol customized for file systems that are used as scalable infrastructure for Web server farms. The protocol takes advantage of the Web's relaxed consistency semantics to reduce latencies and network overhead. Our hybrid approach preserves strong consistency for concurrent write sharing with time-based consistency and push caching for readers (Web servers). Using simulation, we compare our approach to the Andrew file system and the sequential consistency file system protocols we propose to replace     

代理Web Cache性能分析

采用WebCache技术提高当前Internet性能已成为一个主流的研究领域,其功能原理就象处理器和文件系统中的多级高速缓存一样。大规模Web高速缓存系统已成为许多国家Internet基础设施的重要组成部分。该文从三个不同访问规模的代理WebCache的跟踪日志出发,分析了WebCache的用户访问模式、Cache命中率、Cache服务器处理延迟等统计特征,提出基于分布式共享RAM和外存储结合的两级协同WebCache集群技术,可以提供可扩展的高性能并行Web高速缓存服务。     

SemWebDL: A privacy-preserving Semantic Web infrastructure for digital libraries

Recent advances in digital libraries have been closely intertwined with advances in Internet technologies. With the advent of the Web, digital libraries have been able to reach constituencies previously unanticipated. Because of the wide deployability of Web-accessible digital libraries, the potential for privacy violations has also grown tremendously. The much touted Semantic Web, with its agent, service, and ontology technologies, is slated to take the Web to another qualitative level in advances. Unfortunately, these advances may also open doors for privacy violations in ways never seen before. We propose a Semantic Web infrastructure, called SemWebDL, that enables the dynamic composition of disparate and autonomous digital libraries while preserving user privacy. In the proposed infrastructure, users will be able to pose more qualitative queries that may require the ad hoc collaboration of multiple digital libraries. In addition to the Semantic Web-based infrastructure, the quality of the response would rest on extraneous information in the form of a profile. We introduce the concept of communities to enable subject-based cooperation and search speedup. Further, digital libraries heterogeneity and autonomy are transcended by a layered Web-service-based infrastructure. Semantic Web-based digital library providers would advertise to Web services, which in turn are organized in communities accessed by users. For the purpose of privacy preservation, we devise a three-tier privacy model consisting of user privacy, Web service privacy, and digital library privacy that offers autonomy of perspectives for privacy definition and violation. We propose an approach that seamlessly interoperates with potentially conflicting privacy definitions and policies at the different levels of the Semantic Web-based infrastructure. A key aspect in the approach is the use of reputations for outsourcing Web services. A Web service reputation is associated with its behavior with regard to privacy preservation. We developed a technique that uses attribute ontologies and information flow difference to collect, evaluate, and disseminate the reputation of Web services.     

A Web caching primer

The article provides a primer on Web resource caching, one technology used to make the Web scalable. Web caching can reduce bandwidth usage, decrease user-perceived latencies, and reduce Web server loads transparently. As a result, caching has become a significant part of the Web's infrastructure. Caching has even spawned a new industry: content delivery networks, which are also growing at a fantastic rate. Readers familiar with relatively advanced Web caching topics such as the Internet Cache Protocol (ICP), invalidation, and interception proxies are not likely to learn much here. Instead, the article is designed for the general audience of Web users. Rather than a how-to guide to caching technology deployment, it is a high-level argument for the value of Web caching to content consumers and producers. The article defines caching, explains how it applies to the Web, and describes when and why it is useful     

Adapting multimedia Internet content for universal access

Content delivery over the Internet needs to address both the multimedia nature of the content and the capabilities of the diverse client platforms the content is being delivered to. We present a system that adapts multimedia Web documents to optimally match the capabilities of the client device requesting it. This system has two key components. 1) A representation scheme called the InfoPyramid that provides a multimodal, multiresolution representation hierarchy for multimedia. 2) A customizer that selects the best content representation to meet the client capabilities while delivering the most value. We model the selection process as a resource allocation problem in a generalized rate distortion framework. In this framework, we address the issue of both multiple media types in a Web document and multiple resource types at the client. We extend this framework to allow prioritization on the content items in a Web document. We illustrate our content adaptation technique with a web server that adapts multimedia news stories to clients as diverse as workstations, PDA's and cellular phones     

Rule-based Adaptation of Web Information Systems

Mobile devices provide a variety of ways to access information resources available on the Web and a high level of adaptability to different aspects of the context (such as the device capabilities, the network QoS, the user preferences, and the location) is strongly required in this scenario. In this paper, we present a rule-based approach supporting the automatic adaptation of content delivery in Web Information Systems. The approach relies on the general notions of profile and configuration. The former is used to model a variety of context characteristics in a uniform way. The latter describes, in abstract terms, how to build the various levels of a suitable Web interface (content, navigation and presentation). We propose an original notion of adaptation rule that can be used to specify, in a declarative way, how to build a configuration that satisfies the requirements of adaptation for a profile. The evaluation process defined for these rules supports: (1) the handling of many separately specified adaptation requirements according to different aspects of the context, possibly not fixed in advance, and (2) their integration into one coherent recipe for adaptation. We also describe the architecture and functionality of a prototype implementing the proposed approach and illustrate experimental results supporting its flexibility and efficiency. A preliminary version of this paper appears in the Proceedings of Seventh International Conference on Mobile Data Management (MDM’06) Nara, Japan, May 10–12, 2006.     

Design, implementation, and evaluation of differentiated caching services

With the dramatic explosion of online information, the Internet is undergoing a transition from a data communication infrastructure to a global information utility. PDAs, wireless phones, Web-enabled vehicles, modem PCs, and high-end workstations can be viewed as appliances that "plug-in" to this utility for information. The increasing diversity of such appliances calls for an architecture for performance differentiation of information access. The key performance accelerator on the Internet is the caching and content distribution infrastructure. While many research efforts addressed performance differentiation in the network and on Web servers, providing multiple levels of service in the caching system has received much less attention. It has two main contributions. First, we describe, implement, and evaluate an architecture for differentiated content caching services as a key element of the Internet content distribution architecture. Second, we describe a control-theoretical approach that lays well-understood theoretical foundations for resource management to achieve performance differentiation in proxy caches. An experimental study using the Squid proxy cache shows that differentiated caching services provide significantly better performance to the premium content classes.     

具有服务质量保证的Web服务器的设计

目前的因特网正从提供单一的数据传送服务转化为提供各种商业和多媒体的服务,为了在因特网上提供端到端的QoS保障,仅靠在网络的传输和路由方面的改进是不够的,服务器的效率和响应速度也是瓶颈之一。讨论了当前Web服务器设计的一些缺陷,提出了一些解决方法并解释了各个模块的实现机制。     

Effektive Handhabung von Service-Informationen im Internet der Dienste

Business Webs apply the idea of value networks to the WWW. The underlying delivery platform is commonly referred to as the Internet of Services and will certainly have to deal with a great variety and amount of information about services along several service information dimensions. As soon as brokerage, discovery, or community feedback parts are decentralized, there emerge a number of service information challenges (modeling the information in a holistic way, documentation, interlinkage, tool interoperability, distributed querying, inconsistent information, and cooperation of different stakeholders). In this paper, we propose to counter such service information challenges by two artifacts. First, we contribute a Service Ontology based on a sound and rigid foundational ontology. The Service Ontology provides a holistic and consistent way of capturing service information. We apply the recommendations of the W3C Semantic Web Activity whose recent standardization has already opened new possibilities for tool interoperability, interlinkage of information, and distributed querying on the web. However, building and prescribing an ontology in standardized languages is not enough to address all service information challenges. Therefore, as a second contribution, we provide a method around the ontology including a governance framework, guidelines for applying the W3C Semantic Web recommendations, a lifecycle-spanning tool chain, and different levels of applicability. We label our method Semantic Business Web approach, since we build on W3C Semantic Web standards, use and extend them in the Business Web setting. Both artifacts are constructed in an interdisciplinary way by experts participating in the German lighthouse project THESEUS/TEXO. The project’s scenario also serves as a proof of concept evaluation of the artifacts.     

Supporting high-quality video streaming with SDN-based CDNs

Videos and other multimedia contents become increasing popular among users of the Internet nowadays. With the improvement of underlying infrastructure of the Internet, users are allowed to enjoy video contents with much higher quality than last decade. Content delivery networks (CDNs) are a type of content hosting solution that widely used across the Internet. Content providers offload the task of content hosting to CDN providers and redirect users’ requests to CDNs. Video contents, especially high quality videos at real-time has occupying a major part of the Internet traffic. It is challenging to handle such workloads even for a large- scale CDN. Load balancing algorithms are critical to address this issue. However, traditional load balancing algorithms such as round-robin and randomization are unaware of user side requirements. Therefore, it is not uncommon that requests for high-quality videos at real-time are not satisfied. In this paper, we try to fulfill such requests by integrating software-defined networking technology with CDN infrastructure. We also propose revised load balancing algorithms and develop simulations to verify our approaches. The results show that the proposed algorithms achieve much higher user satisfaction in bandwidth-idle environments.     

The Web is not yet suitable for learning

Many sites on the Web refer to themselves as courses. Doing so is popular at present, with an ever increasing number of these courses cropping up everywhere. In some universities, administrators pressure the faculty to provide such courses without offering guidelines for how the Internet might best be used for learning. We've looked at many such courses and come away greatly disappointed. Most of these courses provide little in the way of interaction. Our concern is with situations in which the Web site is intended to be the primary delivery method for learning, not when it is a supplement to learning delivered mainly in other ways, such as through lectures. We are not suggesting that other ways of delivering learning-such as through lectures-are adequate. Distance learning is an important approach for future education, but not as it is currently delivered on the Web     

Web content adaptation to improve server overload behavior

This paper presents a study of Web content adaptation to improve server overload performance, as well as an implementation of a Web content adaptation software prototype. When the request rate on a Web server increases beyond server capacity, the server becomes overloaded and unresponsive. The TCP listen queue of the server's socket overflows exhibiting a drop-tail behavior. As a result, clients experience service outages. Since clients typically issue multiple requests over the duration of a session with the server, and since requests are dropped indiscriminately, all clients connecting to the server at overload are likely to experience connection failures, even though there may be enough capacity on the server to deliver all responses properly for a subset of clients. In this paper, we propose to resolve the overload problem by adapting delivered content to load conditions to alleviate overload. The premise is that successful delivery of a less resource intensive content under overload is more desirable to clients than connection rejection or failures.The paper suggests the feasibility of content adaptation from three different viewpoints; (a) potential for automating content adaptation with minimal involvement of the content provider, (b) ability to achieve sufficient savings in resource requirements by adapting present-day Web content while preserving adequate information, and (c) feasibility to apply content adaptation technology on the Web with no modification to existing Web servers, browsers or the HTTP protocol.     

语义网的研究与应用

语义网是互联网研究者对下一代互联网的称谓,是对现有互联网扩展。通过在信息中加入表示其含义（即语义）的内容,使计算机能够理解和处理,便于人和计算机之间的交互与合作。目前对语义网已经进行了很多研究,并有了些应用,通过的研究与分析,探索语义网及其技术应用。     

Federated search of scientific literature

The Internet of the 21st Century will radically transform how we interact with knowledge. The rise of the World Wide Web and the information infrastructure have rapidly developed the technologies of collections for independent communities. In the future, online information will be dominated by small collections. The information infrastructure must similarly be radically different to support indexing of community collections and searching across such small collections. Users will consider themselves to be navigating in the Interspace, across logical spaces of semantic indexes, rather than in the Internet, across physical networks of computer servers. The digital libraries initiative (DLI) project at the University of Illinois at Urbana-Champaign (UIUC) was one of six sponsored by the NSF, DARPA, and NASA from 1994 through 1998. The goal was to develop widely usable Web technology to effectively search technical documents on the Internet. This article details their efforts     

Web QoS及其保证方法

Internet的服务模式正由传统的数据通信与信息浏览向电子交易与服务转变,仅靠网络QoS机制并不能完全解决端到端的QoS控制问题。Web服务器系统作为核心设施,必须同样具备建立和支持QoS的机制与策略,对不同的用户或HTTP请求提供区分服务和性能保证。文中综述了Web QoS的发展情况、研究现状以及保证方法(包括请求分类机制的划分方法、Web服务供应商的Web系统解决方案以及无线网络的保证方法),并分析了进一步的研究方向。     

Personalizable edge services for Web accessibility

Web Content Accessibility guidelines by W3C (W3C Recommendation, May 1999. ) provide several suggestions for Web designers regarding how to author Web pages in order to make them accessible to everyone. In this context, this paper proposes the use of edge services as an efficient and general solution to promote accessibility and breaking down the digital barriers that inhibit users with disabilities to actively participate to any aspect of society. The idea behind edge services mainly affect the advantages of a personalized navigation in which contents are tailored according to different issues, such as client’s devices capabilities, communication systems and network conditions and, finally, preferences and/or abilities of the growing number of users that access the Web. To meet these requirements, Web designers have to efficiently provide content adaptation and personalization functionalities mechanisms in order to guarantee universal access to the Internet content. The so far dominant paradigm of communication on the WWW, due to its simple request/response model, cannot efficiently address such requirements. Therefore, it must be augmented with new components that attempt to enhance the scalability, the performances and the ubiquity of the Web. Edge servers, acting on the HTTP data flow exchanged between client and server, allow on-the-fly content adaptation as well as other complex functionalities beyond the traditional caching and content replication services. These value-added services are called edge services and include personalization and customization, aggregation from multiple sources, geographical personalization of the navigation of pages (with insertion/emphasis of content that can be related to the user’s geographical location), translation services, group navigation and awareness for social navigation, advanced services for bandwidth optimization such as adaptive compression and format transcoding, mobility, and ubiquitous access to Internet content. This paper presents Personalizable Accessible Navigation (Pan) that is a set of edge services designed to improve Web pages accessibility, developed and deployed on top of a programmable intermediary framework. The characteristics and the location of the services, i.e., provided by intermediaries, as well as the personalization and the opportunities to select multiple profiles make Pan a platform that is especially suitable for accessing the Web seamlessly also from mobile terminals.

The evolution of Web-caching markets

Internet businesses lose billions of dollars each year because of slow and failed Web services, and new companies and coalitions have rushed to provide the worldwide content caching that can help recapture this lost revenue. Although the media has often characterized these companies as trailblazers in the e-commerce revolution, they are merely exploiting a temporary niche along the path to Internet infrastructure commoditization and distributed e-markets. The current players have a chance to succeed, but the future belongs to innovators in the distributed storage and compute online commodities markets