基于XML的数据库查询体系设计

该文从该问题出发,提出了把数据库表变换为XML文档实施数据的查询这一解决思路。该文首先对SAX、DOM、XPath 3种实现XML查询技术的原理进行了分析,阐述了3种技术的优缺点及适用范围,提出了把XPath与DOM相结合的一种灵活简单的XML查询方案,并且构建了XML查询应用模型。     

改进的基于小枝模式的匹配算法——cTwigStack

给定一个小枝模式查询,如何快速地在XML数据集中找到所有感兴趣的信息,已成为当前研究的热点。针对TwigStack算法在处理含有父子节点的情况下会产生大量的中间结果等问题,通过栈来对非叶子节点缓存和对叶子节点延迟输出的思想,提出了一种改进的小枝模式匹配算法--cTwigStack。采用Treebank数据集进行测验,结果表明该算法不仅仅在处理祖孙/后继节点时能使输出结果的准确性达到最优,而且在处理父子节点时,相对目前提出的算法,也是非常高效的。     

Efficient Mining of Frequent Closed XML Query Pattern

Previous research works have presented convincing arguments that a frequent pattern mining algorithm should not mine all frequent but only the closed ones because the latter leads to not only more compact yet complete result set but also better efficiency. Upon discovery of frequent closed XML query patterns, indexing and caching can be effectively adopted for query performance enhancement. Most of the previous algorithms for finding frequent patterns basically introduced a straightforward generate-and-test strategy. In this paper, we present SOLARIA＊, an efficient algorithm for mining frequent closed XML query patterns without candidate maintenance and costly tree-containment checking. Efficient algorithm of sequence mining is involved in discovering frequent tree-structured patterns, which aims at replacing expensive containment testing with cheap parent-child checking in sequences. SOLARIA＊ deeply prunes unrelated search space for frequent pattern enumeration by parent-child relationship constraint. By a thorough experimental study on various real-life data, we demonstrate the efficiency and scalability of SOLARIA＊ over the previous known alternative. SOLARIA＊ is also linearly scalable in terms of XML queries＇ size.     

Axiomatizing the Logical Core of XPath 2.0

The first aim of this paper is to present the logical core of XPath 2.0: a logically clean, decidable fragment, which includes most navigational features of XPath 2.0 (complex counting conditions and data joins are not supported, as they lead to undecidability). The second aim is to provide a list of equations completely axiomatizing query equivalence in this language (i.e., all other query equivalences can be derived from these). A preliminary version of this paper was published in the proceedings of ICDT 2007. We would like to thank Jan Hidders for pointing us to the interesting question of stronger forms of completeness (cf. Sect. 4.3). We would also like to thank the anonymous reviewers for their extensive comments, which have greatly improved the quality of the paper. The first author is supported by NWO grant 639.021.508.     

Optimizing XML queries: Bitmapped materialized views vs. indexes

Optimizing queries using materialized views has not been addressed adequately in the context of XML due to the many limitations associated with the definition and usability of materialized views in traditional XML query evaluation models.     

代码生成技术在MDA中的实现

针对如何将具体的业务模型转换为应用程序代码的问题,提出了一个采用XSLT技术的代码生成器设计方案,用来实现MDA中的自动代码生成。从介绍代码生成器的输入文件入手,讨论了代码生成器的处理原理,最后举了一个采用XSLT技术的代码生成器生成代码的例子。     

Web信息抽取系统的设计

为了获取分散Web页面中隐含信息,设计了Web信息抽取系统。该系统首先使用一种改进的HITS主题精选算法进行信息采集;然后对Web页面的HTML结构进行文档的数据预处理;最后,基于DOM树的XPath绝对路径生成算法来获取被标注结点的XPath表达式,并使用XPath语言结合XSLT技术来编写抽取规则,从而得到结构化的数据库或XML文件,实现了Web信息的定位和抽取。通过一个购物网站的抽取实验证明,该系统的抽取效果良好,可以实现相似Web页面的批量抽取。     

Independence of Containing Patterns Property and Its Application in Tree Pattern Query Rewriting Using Views

We show that several classes of tree patterns observe the independence of containing patterns property, that is, if a pattern is contained in the union of several patterns, then it is contained in one of them. We apply this property to two related problems on tree pattern rewriting using views. First, given view V and query Q, is it possible for Q to have an equivalent rewriting using V which is the union of two or more tree patterns, but not an equivalent rewriting which is a single pattern? This problem is of both theoretical and practical importance because, if the answer is no, then, to find an equivalent rewriting of a tree pattern using a view, we should use more efficient methods, such as the polynomial time algorithm of Xu and Özsoyoglu (2005), rather than try to find the union of all contained rewritings (which takes exponential time in the worst case) and test its equivalence to Q. Second, given a set S of views, we want to know under what conditions a subset S′ of S is redundant in the sense that for any query Q, the contained rewritings of Q using the views in S′ are contained in those using the views in S???S′. Solving this problem can help us to, for example, choose the minimum number of views to be cached, or better design the virtual schema in a mediated data integration system, or avoid repeated calculation in query optimization. For the first problem, we identify several classes of tree patterns for which the equivalent rewriting can be expressed as a single tree pattern. For the second problem, we present necessary and sufficient conditions for S′ to be redundant with respect to some classes of tree patterns. For both problems we consider extension to cases where there are rewritings using the intersection of multiple views and/or where a schema graph is present.     

基于XML的异构数据集成模式的研究

随着信息技术的发展,任何一个独立单位都有可能成为一个异构的数据源.为实现企业异构数据库问信息的共享和集成,对数据集成的原理以及主要技术进行了研究,重点分析了XML与数据库之间的映射、XML文档存储模式、将XML查询转化为SQL的查询转换问题以及如何将关系数据发布为XML文档,并提出了相应的解决方法.该方案简单易行,保证了各系统仍然按照原来的方式运行,只需要进行信息交换时通过转换接口把本地数据库数据转换成XML文档即可.     

利用XML和Excel设计动态通用报表系统的新方法

提出一种利用XML和Excel设计动态通用报表系统的新方法。首先对Excel报表模板进行分解,生成报表模板的报表信息、架构信息和映射信息,再根据统计模板生成统计分析信息,这些信息均以XML文档的形式存入数据库。在系统运行时,将用户上报的Excel文件中的报表数据提取出来,以XML文档的形式存入数据库。然后结合XPath和XQuery对报表数据进行统计分析,得到统计报表数据。最后将统计报表数据组装为Excel文件输出给用户。采用这种方法设计的报表系统动态灵活、通用性强。