RDF数据的并行处理及性能评价

语义Web作为数据之网不断汇集并组织Web信息,相关应用因此面临着对语义Web所含大规模RDF数据高效访问的挑战.利用并行处理技术提高性能是一种解决之道,其核心是RDF数据的放置策略和并行查询处理.已有工作尚未系统研究RDF数据放置策略的分类与特点,及其对查询处理性能的影响.分析了RDF数据上各类数据放置幕略及其对查询处理性能影响,通过LUBM测试基准结果分析评价了典型的RDF并行处理策略(数据放置策略及相应并行查询处理)的实际性能,为提出更有效的并行处理策略奠定了基础.     

RDF 数据查询处理技术综述

随着语义网以及信息抽取技术等研究的发展,Web上涌现出越来越多的RDF数据,海量RDF数据的管理,已经成为学术界和工业界研究的热点之一。从RDF数据集形态及RDF数据组织存储两个维度以及查询表述、查询处理、查询优化等方面,深入地分析和比较了RDF数据查询处理方法,并在此基础上提出了未来研究的方向和挑战。     

A formal approach for graphically building fuzzy XML model

eXtensible Markup Language (XML) has been the de facto standard of data representation and exchange over the Web. In addition, imprecise and uncertain data are inherent in the real world. Although fuzzy data have been extensively investigated in the context of the relational model, the classical relational database model and its fuzzy extension to date do not satisfy the need of modeling complex objects with imprecision and uncertainty on the Web. On the basis of possibility theory, this paper concentrates on fuzzy information modeling in the fuzzy XML model and the fuzzy IFO model. In particular, the formal approach to mapping a fuzzy IFO model to a fuzzy document-type definition model is developed.     

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.     

语言变量模糊本体的表示与构建

语言变量模糊本体是语言变量在语义Web中的明确的规范化说明,有利于模糊系统与语义Web的结合,使得语义web更加方便地处理模糊信息。通过引入语言变量模糊本体的概念,研究使用RDF表示模糊本体的方法,将本体与模糊概念表示为“资源”。进而以工业洗衣机的模糊控制为例,提出从模糊系统构造语言变量模糊本体的过程。     

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·     

基于RDFS的数据结构描述

资源描述框架(RDF)/资源描述框架模式(RDFS)是语义互联网架构中的技术。尽管XML/RDF数据库正迅速地发展,关系型数据库仍是目前企业级应用的首选。针对在应用中混合使用关系型数据库管理系统和RDF/RDFS的问题,该文提出了关系数据库表结构的RDFS定义方法以及在此基础上的数据获取方式,目的是在关系数据库与应用系统之间建立基于RDFS的抽象数据结构描述,实现数据结构的可配置性以及RDF数据的可访问性。     

基于RDF句子的语义网文档搜索

语义网文档搜索是发现语义网数据的重要手段.针对传统信息检索方法的不足,提出基于RDF句子的文档词向量构建方法.首先,文档被看作RDF句子的集合,从而在文档分析和索引时能够保留基于RDF句子的结构信息.其次,引入资源的权威描述的定义,能够跨越文档边界搜索到语义网中互连的数据.此外,扩展了传统的倒排索引结构,使得系统能够提取出更加便于阅读和理解的片段.在大规模真实数据集上的实验表明,该方法可以显著地提高文档检索的效率,在可用性上具有明显的提升.     

A multigranularity locking model for RDF

The advent of Linked Data is spurring the deployment of applications that use the RDF data model at the information tier. In addition to querying RDF data, there is also the requirement for online updates with suitable concurrency control. Client sessions in Web applications are organized as transactions involving requests that read and write shared data. Executing concurrently, these sessions may invalidate each other’s data. This paper presents a locking model, which is a variant of multigranularity locking protocol (MGL), to address isolation between transactions that manipulate RDF data. Four “hierarchically” related granules are defined, as well as new read/write operations and their corresponding lock modes, specifically created for the RDF data model. These new operations allow greater concurrency than the classical read/write operations in relational databases. We assessed the performance of the proposed locking model through model simulation.     

Everything you always wanted to know about blank nodes

In this paper we thoroughly cover the issue of blank nodes, which have been defined in RDF as ‘existential variables’. We first introduce the theoretical precedent for existential blank nodes from first order logic and incomplete information in database theory. We then cover the different (and sometimes incompatible) treatment of blank nodes across the W3C stack of RDF-related standards. We present an empirical survey of the blank nodes present in a large sample of RDF data published on the Web (the BTC-2012 dataset), where we find that 25.7% of unique RDF terms are blank nodes, that 44.9% of documents and 66.2% of domains featured use of at least one blank node, and that aside from one Linked Data domain whose RDF data contains many “blank node cycles”, the vast majority of blank nodes form tree structures that are efficient to compute simple entailment over. With respect to the RDF-merge of the full data, we show that 6.1% of blank-nodes are redundant under simple entailment. The vast majority of non-lean cases are isomorphisms resulting from multiple blank nodes with no discriminating information being given within an RDF document or documents being duplicated in multiple Web locations. Although simple entailment is NP-complete and leanness-checking is coNP-complete, in computing this latter result, we demonstrate that in practice, real-world RDF graphs are sufficiently “rich” in ground information for problematic cases to be avoided by non-naive algorithms.     

个性化搜索引擎

随着网络上的知识不断暴涨，用户要求快速、有效地获取网络资源，该文提出了一种通过产生用户动态偏好来达到个性化搜索的方法，通过对搜索结果作一种基于内容的按名分类算法来为用户创建一个以RDF的形式表达的动态偏好。通过对RDF偏好文件的聚类来发现用户社区，产生相应的用户社区偏好。在搜索过程中，通过对该用户及其所属社区的偏好来分析。对搜索结果按重要性排序，达到了用户个性化搜索的目的。     

应用于电子商务的语义Web核心语言分析

到目前为止已有多种基于语义Web的语言，这些语言实现了基于Web的知识表示、共享和重用。重点分析了语义Web的几种语言：XML规范簇、RDF、RDF Schema、DAML OIL。在此基础上给出了语义Web技术的重要应用——电子商务中核心语言的分层结构。该结构中XML规范簇完成了数据描述功能，RDF用于描述元数据，RDF Schema提供了基本的本体原语，DAML OIL提供了推理功能，利用这些语言，可以实现电子商务中数据描述的统一性、通用性及互操作性。     

Formal translation from fuzzy EER model to fuzzy XML model

XML has been the de facto standard of data representation and exchange over the Web. In addition, fuzzy data are inherent in the real-world applications. Although fuzzy information has been extensively investigated in the context of relational database model, the classical relational database model and its fuzzy extension to date do not satisfy the need of modeling and processing complex objects with imprecision and uncertainty on the Web. Based on fuzzy sets, this paper concentrates on fuzzy information modeling in the EER (enhanced entity-relationship or extended entity-relationship) model and the fuzzy XML model. In particular, the formal approach to mapping the fuzzy EER model to the fuzzy DTD (document type definition) model is developed.