一种高效的RDF图模式匹配算法

随着越来越多的信息被表示为RDF格式,如何高效地对RDF信息进行分发和过滤成为一个重要的问题·在语义Web环境下的信息分发系统中,输入的RDF信息需要和大量的用户订阅条件进行匹配,而用户的订阅条件可以被表示为RDF图模式·根据RDF图的特点,并对其增加了一些约束,设计了一种新的RDF图模式匹配算法·实验结果表明,该算法的匹配效率远远高于传统的图模式匹配算法·     

An integration site for Semantic Web metadata

The Semantic Web has motivated many communities to provide data in a machine-readable format. However, the available data has not been utilized to far to the extent possible. The data, which has been created by a large number of people, is dispersed across the Web. Creating the data without central coordination results in RDF of varying quality and makes it obligatory to cleanse the collected data before integration. The SECO system presented in this paper harvests RDF files from the Web and consolidates the different data sets into a coherent representation aligned along an internal schema. SECO provides interfaces for humans to browse and for software agents to query the data repository. In this paper, we describe the characteristics of RDF data available online, the architecture and implementation of the SECO application, and discuss some of the experienced gained while collecting and integrating RDF on the Web.     

System |Π: A Native RDF Repository Based on the Hypergraph Representation for RDF Data Model

RDF is the data interchange layer for the Semantic Web. In order to manage the increasing amount of RDF data, an RDF repository should provide not only the necessary scalability and efficiency, but also sufficient inference capabilities. Though existing RDF repositories have made progress towards these goals, there is still ample space for improving the overall performance. In this paper, we propose a native RDF repository, System Π, to pursue a better tradeoff among system scalability, query efficiency, and inference capabilities. System Π takes a hypergraph representation for RDF as the data model for its persistent storage, which effectively avoids the costs of data model transformation when accessing RDF data. Based on this native storage scheme, a set of efficient semantic query processing techniques are designed. First, several indices are built to accelerate RDF data access including a value index, a labeling scheme for transitive closure computation, and three triple indices. Second, we propose a hybrid inference strategy under the pD ^* semantics to support inference for OWL-Lite with a relatively low computational complexity. Finally, we extend the SPARQL algebra to explicitly express inference semantics in logical query plan by defining some new algebra operators. In addition, MD5 hash value of URI and schema level cache are introduced as practical implementation techniques. The results of performance evaluation on the LUBM benchmark and a real data set show that System Π has a better combined metric value than other comparable systems.     

SW-Store: a vertically partitioned DBMS for Semantic Web data management

Efficient management of RDF data is an important prerequisite for realizing the Semantic Web vision. Performance and scalability issues are becoming increasingly pressing as Semantic Web technology is applied to real-world applications. In this paper, we examine the reasons why current data management solutions for RDF data scale poorly, and explore the fundamental scalability limitations of these approaches. We review the state of the art for improving performance of RDF databases and consider a recent suggestion, “property tables”. We then discuss practically and empirically why this solution has undesirable features. As an improvement, we propose an alternative solution: vertically partitioning the RDF data. We compare the performance of vertical partitioning with prior art on queries generated by a Web-based RDF browser over a large-scale (more than 50 million triples) catalog of library data. Our results show that a vertically partitioned schema achieves similar performance to the property table technique while being much simpler to design. Further, if a column-oriented DBMS (a database architected specially for the vertically partitioned case) is used instead of a row-oriented DBMS, another order of magnitude performance improvement is observed, with query times dropping from minutes to several seconds. Encouraged by these results, we describe the architecture of SW-Store, a new DBMS we are actively building that implements these techniques to achieve high performance RDF data management.     

Searching and browsing Linked Data with SWSE: The Semantic Web Search Engine

In this paper, we discuss the architecture and implementation of the Semantic Web Search Engine (SWSE). Following traditional search engine architecture, SWSE consists of crawling, data enhancing, indexing and a user interface for search, browsing and retrieval of information; unlike traditional search engines, SWSE operates over RDF Web data – loosely also known as Linked Data – which implies unique challenges for the system design, architecture, algorithms, implementation and user interface. In particular, many challenges exist in adopting Semantic Web technologies for Web data: the unique challenges of the Web – in terms of scale, unreliability, inconsistency and noise – are largely overlooked by the current Semantic Web standards. Herein, we describe the current SWSE system, initially detailing the architecture and later elaborating upon the function, design, implementation and performance of each individual component. In so doing, we also give an insight into how current Semantic Web standards can be tailored, in a best-effort manner, for use on Web data. Throughout, we offer evaluation and complementary argumentation to support our design choices, and also offer discussion on future directions and open research questions. Later, we also provide candid discussion relating to the difficulties currently faced in bringing such a search engine into the mainstream, and lessons learnt from roughly six years working on the Semantic Web Search Engine project.     

基于分布RDF(S)模型的信息查询与集成

在Web应用环境中,可以通过RDF(S)形式描述企业领域内分布信息资源的语义,以提高信息查询的准确性.提出了描述分布异构RDF(S)的分布RDF(S)模型,并基于这一模型给出了实现分布RDF(S)查询的方法,此查询方法既能实现实例层次的查询,也能实现概念层次的查询.基于这一方法,用户能够以统一的形式来查询,获取相关的信息资源,同时还可以实现分布RDF(S)的集成.     

基于语义推理的DSS模型研究与应用

基于语义网理论建立基于语义推理的DSS模型。该模型引用W3C提出的资源描述框架（RDF）以描述业务领域中各要素,形成领域本体。并对领域中业务数据进行语义标注,构建事实库。在所构建事实库的基础上,系统根据预设规则进行推理,以达到决策支持的目的。最后基于以上方法对施工项目设备推荐领域进行实例建模,建立设备推荐系统。该系统将Semantic Web与Ontology理论引入到施工项目领域,以解决施工项目过程中存在的设备选型推荐问题,并作为语义Web理论在该领域内应用的一次尝试。     

Making agents secure on the semantic Web

Agents were designed to collaborate and share information. While highly desirable for interoperability, this feature is scary from the security perspective. Illegal inferences, supported by semantic Web technology and ontologies, might enable users to access unauthorized information. In addition to semantic associations and replicated data with different sensitivity, malicious agents could also exploit statistical inferences. Although each agent in a system might behave in a desired and secure way, their combined knowledge could be used to disclose sensitive data. The research community must therefore develop and implement techniques that allow control over released data. To answer the questions related to information availability (scalability), data correctness (integrity), and access control in the presence of illegal inferences and undesired collaborations (confidentiality), researchers in semantic Web technologies (XML, RDF, DAML, and multiagent systems) and information system security need to collaborate. Indeed, given the Web's openness, dynamic nature, and diverse user population, developing secure Web services will require the collaboration of experts in different fields from both industry and academia. In turn, the intelligent Web of the future will facilitate unheard of support for collaborations and information management.     

Atlas: Storing, updating and querying RDF(S) data on top of DHTs

The RDF(S) data model has been proposed for encoding metadata about Web resources. As more and more Web resources are annotated using RDF(S), there is an urgent need for efficiently dealing with this large volume of data. In this paper, we present Atlas, a peer-to-peer system for storing, updating and querying RDF(S) data. The Atlas system has been built using the distributed hash table Bamboo. Atlas was developed in the context of project OntoGrid, where it was used as a distributed repository for RDF(S) metadata describing Grid services and resources. The development of Atlas continues in other projects that our group participates currently. This paper gives an overview of the most recent version of Atlas and discusses a representative application.     

The Semantic Web: the roles of XML and RDF

XML and RDF are the current standards for establishing semantic interoperability on the Web, but XML addresses only document structure. RDF better facilitates interoperation because it provides a data model that can be extended to address sophisticated ontology representation techniques. We explain the role of ontologies in the architecture of the Semantic Web. We then briefly summarize key elements of XML and RDF, showing why using XML as a tool for semantic interoperability will be ineffective in the long run. We argue that a further representation and inference layer is needed on top of the Web's current layers, and to establish such a layer, we propose a general method for encoding ontology representation languages into RDF/RDF schema. We illustrate the extension method by applying it to Ontology Interchange Language, an ontology representation and inference language     

基于RSS的个性化信息服务研究

由于绝大部分Web信息都是非结构化的,使得现有的个性化服务系统在用户建模时面临着大量的信息预处理工作,并且在个性化推送方式上缺乏动态性和时效性.将个性化技术与RSS技术相结合,首先提出基于RSS技术的个性化信息服务系统的架构,该架构在建立用户兴趣模型和信息推送中揉合了RSS技术;然后给出该架构中几个关键问题的解决方法;最后通过一个试验实例,说明该架构的可行性.     

UDDI技术及其在校园网中的应用

基于UDDI技术和Web Service 应用架构,本文提出了利用高校私有UDDI注册中心进行校园信息系统的集成,并对UDDI信息模型结构以及基于私有UDDI注册中心的高校系统集成的主体架构的设计与实现进行了详细的分析研究.     

基于轻量级框架组合的农业气象信息系统

为了提高农业气象信息服务的服务质量和信息覆盖面,以及对信息的采编和发布实行统一管理,通过构建一套农业气象信息系统来实现这一目的,该系统基于webservice的服务架构,并应用轻量级JEE框架组合-SJH来实现各个层面的业务需求和应用整合。在实际应用过程中,SJH框架组合能够方便快捷地建立起Web应用系统,并且在整合其他应用技术上具有很大的优势。