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针对OBDA的SPARQL OPTIONAL的有效处理Efficient Handling of SPARQL OPTIONAL for OBDA |
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| 课程网址: | http://videolectures.net/iswc2018_cogrel_efficient_sparql_obda/ |
| 主讲教师: | Benjamin Cogrel |
| 开课单位: | 博赞博尔扎诺自由大学 |
| 开课时间: | 2018-11-22 |
| 课程语种: | 英语 |
| 中文简介: |  |
| 课程简介: | OPTIONAL is a key feature in SPARQL for dealing with missing information. While this operator is being used extensively, it is also known for its complexity, which can make it challenge to evaluate queries with OPTIONAL efficiently. In this paper, we tackle this challenge in the standard Ontology-Based Data Access (OBDA) setting, where the data is stored in a SQL relational database and is exposed as a virtual RDF graph by the means of an R2RML mapping. We start with a succinct translation of a fragment of SPARQL into Relational Algebra (RA) that fully respects bag semantics and three-valued logic. This translation relies on extensive use of the LEFT JOIN operator and coalesce function. We then propose a number of optimisation techniques for reducing the size and improving the structure of generated SQL queries. Our optimisations capture interactions between JOIN, LEFT JOIN, coalesce and database integrity constraints such as attribute nullability and uniqueness, and foreign key constraints. Finally, we empirically verify effectiveness of our techniques over several OBDA benchmarks. |
| 关 键 词: | SPARQL中处理缺失信息; 运算符被广泛使用; R2RML映射; 虚拟RDF图公开 |
| 课程来源: | 视频讲座网 |
| 数据采集: | 2023-01-11：cyh |
| 最后编审: | 2023-01-11：cyh |
| 阅读次数: | 28 |