共查询到20条相似文献，搜索用时 15 毫秒
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随着语义网的快速发展,为了实现科学数据的共享,越来越多的科学数据被加工发布为关联数据,进而应用于关联查询和关联发现。针对大规模关联数据的管理,本文通过构建 RDF 数据库集群来存储海量数据,设计了基于 SPARQL 端点的联合查询系统来解决用户跨机器透明查询的问题,分析了存储策略和联合查询系统的查询处理相关技术。实际运行表明,本平台易于集成使用,可以实现大规模 RDF 数据的可扩展性存储和有效查询。 相似文献
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Most existing RDF stores, which serve as metadata repositories on the Semantic Web, use an RDBMS as a backend to manage RDF data. This motivates us to study the problem of translating SPARQL queries into equivalent SQL queries, which further can be optimized and evaluated by the relational query engine and their results can be returned as SPARQL query solutions. The main contributions of our research are: (i) We formalize a relational algebra based semantics of SPARQL, which bridges the gap between SPARQL and SQL query languages, and prove that our semantics is equivalent to the mapping-based semantics of SPARQL; (ii) Based on this semantics, we propose the first provably semantics preserving SPARQL-to-SQL translation for SPARQL triple patterns, basic graph patterns, optional graph patterns, alternative graph patterns, and value constraints; (iii) Our translation algorithm is generic and can be directly applied to existing RDBMS-based RDF stores; and (iv) We outline a number of simplifications for the SPARQL-to-SQL translation to generate simpler and more efficient SQL queries and extend our defined semantics and translation to support the bag semantics of a SPARQL query solution. The experimental study showed that our proposed generic translation can serve as a good alternative to existing schema dependent translations in terms of efficient query evaluation and/or ensured query result correctness. 相似文献
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M. Tamer ÖZSU 《Frontiers of Computer Science》2016,10(3):418-432
RDF is increasingly being used to encode data for the semantic web and data exchange. There have been a large number of works that address RDF data management following different approaches. In this paper we provide an overview of these works. This review considers centralized solutions (what are referred to as warehousing approaches), distributed solutions, and the techniques that have been developed for querying linked data. In each category, further classifications are provided that would assist readers in understanding the identifying characteristics of different approaches. 相似文献
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对传感器产生的语义数据流执行复杂推理的能力, 最近已成为语义网社区中的重要研究领域, 而目前大多数RDF流处理系统是以SPARQL (W3C标准RDF查询语言)为基础实现的, 但这些引擎在捕获复杂的用户需求和处理复杂的推理任务方面存在局限性. 针对此问题, 本文结合并扩展了回答集编程(Answer Set Programing, ASP)技术用于对RDF流进行连续的处理. 为了验证本方法的有效性, 首先以智能家居本体为实验对象, 并分析传感器设备间的共有特性及复杂事件以构建本体库; 然后基于本体库产生实例对象, 并通过中间件产生RDF数据流; 接下来通过扩展ASP, 充分利用其表达和推理能力以减少推理时间, 并设计了RDF 流的窗口划分策略等, 然后根据用户的请求, 选择性地进行静态知识库加载等; 最后通过实验与Sparkwave和Laser进行对比, 证明了该方法在延迟和内存上的性能优势. 相似文献
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陈彦 《数字社区&智能家居》2007,2(10):947-949
论文以通用的不依赖于具体RDF平台的SPARQL查询引擎的设计与实现作为研究对象。并从SPARQL语法解析器、引擎系统的优化设计等方面进行了深入的探讨,提出了合理的设计策略和实现方法。 相似文献
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在分析SPARQL标准和基于Jena的开源SPARQL工具ARQ查询引擎源码的基础上,提出了可支持关联查询的扩展SPARQL标准及其设计和实现方案,认真分析了已有的试验成果。 相似文献
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Linked Open Data initiatives have encouraged the publication of large RDF datasets into the Linking Open Data (LOD) cloud, including DBpedia, YAGO, and Geo-Names. Despite the size of LOD datasets and the development of (semi-)automatic methods to create and link LOD data, these datasets may be still incomplete, negatively affecting thus accuracy of Linked Data processing techniques. We acquire query answer completeness by capturing knowledge collected from the crowd, and propose a novel hybrid query processing engine that brings together machine and human computation to execute SPARQL queries. Our system, HARE, implements these hybrid query processing techniques. HARE encompasses several features: (1) a completeness model for RDF that exploits the characteristics of RDF in order to estimate the completeness of an RDF dataset; (2) a crowd knowledge base that captures crowd answers about missing values in the RDF dataset; (3) a query engine that combines on-the-fly crowd knowledge and estimates provided by the RDF completeness model, to decide upon the sub-queries of a SPARQL query that should be executed against the dataset or via crowd computing to enhance query answer completeness; and (4) a microtask manager that exploits the semantics encoded in the dataset RDF properties, to crowdsource SPARQL sub-queries as microtasks and update the crowd knowledge base with the results from the crowd. Effectiveness and efficiency of HARE are empirically studied on a collection of 50 SPARQL queries against the DBpedia dataset. Experimental results clearly show that our solution accurately enhances answer completeness. 相似文献
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针对在SPARQL查询处理中,随着查询图结构逐渐复杂而导致基于图的查询效率愈发低下的问题,通过分析几种资源描述框架（RDF）图的基本结构,提出了一种基于查询图结构切分的子图匹配方法——RSM。首先,将查询图切分为若干结构简单的查询子图,并通过相邻谓词结构索引来定义查询图节点的搜索空间;然后,通过相邻子图结构来缩小搜索空间范围,在数据图中根据搜索空间中的搜索范围找到符合的子图结构;最后,将得到的子图进行连接并作为查询结果输出。将RSM与RDF-3X、R3F、GraSS等主流查询方法作比较,对比了各方法在不同数据集上对于复杂程度不同的查询图的查询响应时间。实验结果充分表明,与其他3种方法相比,在处理结构复杂的查询图时,RSM的查询响应时间更短,具有更高的查询效率。 相似文献
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肖铮 《计算机技术与发展》2020,(5):70-75
以RDF结构为基础的数据网的发展中,高效数据检索成为关键问题之一.形式化查询语言(如SPARQL)因其语法的复杂性及查询本体的相关性阻碍其效用的发挥,迫切需要新的方法或工具实现以自然语言为基础(如关键字检索)的检索.形式化查询语言是检索这类结构化数据的有效方式,用户习惯自然语言为基础的检索方式.因而如何自动将关键词为基... 相似文献
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针对当前资源描述框架(RDF)查询语言查询数据效率不高且不能查全的特点,通过研究关系数据库模式到RDF视图的映射关系,在基于本体的智能检索方法基础上引进分层思想,设计和实现一种单本体数据源环境下的RDF查询引擎,实现隐含语义的发现。实验表明该引擎能较好地实现高效率的语义查询,并具有更大的灵活性和可扩展性。 相似文献
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Navigational features have been largely recognized as fundamental for graph database query languages. This fact has motivated several authors to propose RDF query languages with navigational capabilities. In this paper, we propose the query language nSPARQL that uses nested regular expressions to navigate RDF data. We study some of the fundamental properties of nSPARQL and nested regular expressions concerning expressiveness and complexity of evaluation. Regarding expressiveness, we show that nSPARQL is expressive enough to answer queries considering the semantics of the RDFS vocabulary by directly traversing the input graph. We also show that nesting is necessary in nSPARQL to obtain this last result, and we study the expressiveness of the combination of nested regular expressions and SPARQL operators. Regarding complexity of evaluation, we prove that given an RDF graph G and a nested regular expression E, this problem can be solved in time O(|G||E|). 相似文献