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Web 数据源选择技术   总被引:2,自引:1,他引:1       下载免费PDF全文
在Web数据集成的过程中,如何从大量的Web数据源集合中选择合适数量的数据源,使得在满足特定查询需求的前提下尽可能地减少所需访问的数据源数量,同时保持返回数据结果的高质量,成为Web数据集成中的一个热点问题.以近十几年的研究实践为背景,介绍Web数据源选择的研究沿革及现状,并对Web数据源选择方法进行了归类.分别讨论了基于相关性的和基于质量的数据源选择的研究动机、研究方法和研究成果等,并对相关研究的目标、关键技术、优点和缺点进行了对比分析;最后展望了Web数据源选择未来的研究方向.  相似文献
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针对提供大规模数据查询的Web页面,提出了一种基于站点内页面对比分析的web数据提取方法。在对页面建树和分块的基础上对比分析获得页面数据块,然后利用同结构多页面对比和格式判断提取出数据,最后将数据存入到主据库中。该方法成功运用到多个信息提取系统中,实现了高效、准确的数据提取。  相似文献
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Structured and semi-structured (a.k.a. swept or extruded) hexahedral meshes are used in many types of engineering analysis. In finite element analysis, regions of structured and semi-structured mesh are often connected in an unstructured manner, preventing the use of a globally consistent parametric space to represent these meshes. This paper describes a method for mapping between the parametric spaces of such regions, and methods for representing these regions and interfaces between them. Using these methods, a 57% reduction in mesh storage cost is demonstrated, without loss of any information. These methods have been implemented in the MOAB mesh database component, which provides access to these meshes from both structured and unstructured functions. The total cost for representing structured mesh in MOAB is less than 25 MB per million elements using double-precision vertex coordinates; this is only slightly larger than the space required to store vertex coordinates alone.Sandia is a multiprogram laboratory operated by Sandia corporation, a Lockheed Martin company, for the United States department of energy under contract DE-AC04-94AL85000. This work was performed under the auspices of the U.S. Department of Energy, Office of Advanced Scientific Computing, SciDAL program.  相似文献
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In this paper we propose an approach for deriving a global representation of data sources having different formats and structures. The proposed approach is based on the exploitation of a particular conceptual model for both uniformly representing such data sources and reconstructing both their intra-source and their inter-source semantics. Along with the global representation, our approach returns two support structures which improve the access transparency to stored information, namely, a set of mappings, encoding the transformations carried out during the construction of the global representation, and a set of views, allowing to obtain instances of the concepts of the global representation from instances of the concepts of the input data sources. The paper also describes a prototype which implements the proposed approach.A preliminary and partial version of this paper appears under the title A semi-automatic technique for constructing a global representation of information sources having different formats and structure in the Proceedings of the Conference Database and Expert System Applications (DEXA 2001), Munich, September 2001.  相似文献
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