共查询到18条相似文献,搜索用时 187 毫秒
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基于扩展编码的在线XML文档加载机制 总被引:1,自引:0,他引:1
Webservices应用中存在大量在线XML文档处理的需求,利用现行的XML数据处理方法来处理上述在线文档是一项可行方案,在线文档的加载问题应运而生;目前对XML数据的存储和查询都是基于对XML文档树的某种编码方法,使用扩展编码方法以提高文档更新性能;如何基于扩展编码方法完成对在线文档加载的研究目前还比较少.提出一种新的扩展编码方法,在此编码的基础上,提出一种适合在线XML文档的加载方法,通过统计同模式的XML文档特征和更新特征,一遍解析文档完成扩展编码和加载;实验结果表明,加载效率和更新性能较好. 相似文献
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基于分治策略的XML文档更新计算 总被引:1,自引:0,他引:1
XML文档更新是XML数据管理的重要功能,对XML文档进行插入更新操作时面临编码调整问题,目前大部分编码方案并不能很好支持文档更新。在分析现有编码方案基础上,提出了OMPN(order, maxOrder, parentOrder, nextOrder)编码方案,采用分治策略和迟后更新方法,在插入节点过程中不需要调整编码,在计算资源空闲时,只需调整部分编码就可以完成对XML文档的更新。实验结果表明,基于分治策略和迟后更新方法提高了更新XML文档的性能。 相似文献
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XML已成为各种网络应用中数据存储和数据交换的标准.XML数据管理面临的最大困难在于结构与数据混合存储导致大量数据冗余,这极大地增加了XML数据存储、交换和处理的代价.对XML文档进行压缩可以在一定程度上解决这个问题.但现有XML压缩方法大都仅压缩单文档中的冗余信息.利用XML文档间的相似性,提出一种支持查询的多XML文档压缩存储方法XCluster.XCluster先利用XML有根有序标签树上改进的pq-gram近似距离对XML文档集进行层次聚类;然后合并每个聚类结果子集中文档的结构得到结构代表并进行字典编码压缩;同时合并不同文档内同一标签下的值内容,并根据其数据类型进行相应编码压缩.实验结果表明,在真实和生成的XML多文档数据集上,XCluster比XGrind和XQilla具有更好的压缩效果和查询效率. 相似文献
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XML文档在关系数据库中的规范化存储 总被引:8,自引:0,他引:8
提出了一种存储方法,首先把XML文档映射为泛关系模式,再利用算法DeriveFDs推导出XML键所蕴含的泛关系模式上函数依赖集的规范覆盖,根据此规范覆盖,最后将泛关系模式保持函数依赖地分解为3NF模式集。得到了保持XML键约束的规范化存储模式,实现了XML文档在关系数据库中的规范化存储。实验研究表明文中提出的方法是有效的。 相似文献
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This paper investigates the view update problem for XML views published from relational data.We consider XML views defined in terms of mappings directed by possibly reeursive DTDs compressed into DAGs and stored in relations. We provide new techniques to efficiently support XML view updates specified in terms of XPath expressions with recursion and complex filters.The interaction between XPath recursion and DAG compression of XML views makes the analysis of the XML view update problem rather intriguing.Furthermore,many issues are still open even for relational view updates, and need to be explored.In response to these,on the XML side,we revise the notion of side effects and update semantics based on the semantics of XML views,and present efficient algorithms to translate XML updates to relational view updates. On the relational side,we propose a mild condition on SPJ views,and show that under this condition the analysis of deletions on relational views becomes PTIME while the insertion analysis is NP-complete.We develop an efficient algorithm to process relational view deletions,and a heuristic algorithm to handle view insertions.Finally,we present an experimental study to verify the effectiveness of our techniques. 相似文献
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With the extensive use of XML in applications over the Web, how to update XML data is becoming an important issue because the role of XML has expanded beyond traditional applications in which XML is used for information exchange and data representation over the Web. So far, several languages have been proposed for updating XML data, but they are all based on lower, so-called graph-based or tree-based data models. Update requests are thus expressed in a nonintuitive and unnatural way and update statements are too complicated to comprehend. This paper presents a novel declarative XML update language which is an extension of the XML-RL query language. Compared with other existing XML update languages, it has the following features. First, it is the only XML data manipulation language based on a higher data model. Second, this language can express complex update requests at multiple levels in a hierarchy in a simple and flat way. Third, this language directly supports the functionality of updating complex objects while all other update languages do not support these operations. Lastly, most of existing languages use rename to modify attribute and element names, which is a different way from updates on value. The proposed language modifies tag names, values, and objects in a unified way by the introduction of three kinds of logical binding variables: object variables, value variables, and name variables. 相似文献
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Dynamically Updating XML Data: Numbering Scheme Revisited 总被引:2,自引:0,他引:2
Almost all existing approaches use certain numbering scheme to encode XML elements to facilitate query processing when XML data is stored in databases. For example, under the most popular region-based numbering scheme, the starting and ending positions of an element in a document are used as the code to identify the element so that the ancestor/descendant relationship between two elements can be determined by merely examining their codes. While such numbering scheme can greatly improve query performance, renumbering large amount of elements caused by updates becomes a performance bottleneck if XML documents are frequently updated. Unfortunately, no satisfactory work has been reported for efficient update of XML data. In this paper, we first formalize the XML data update problem by defining the basic operators to support most XML update queries. We then present a new numbering scheme that not only requires minimal code-length in comparison with existing numbering schema but also improves update performance when XML data is frequently updated at arbitrary positions. The fundamental difference between our new scheme and existing ones is that, instead of maintaining the explicit codes for elements, we only store the necessary information and generate the codes when they are needed in query processing. In addition to present the basic scheme, we also discuss some optimization techniques to further reduce the update cost. Results of a comprehensive performance study are provided to show the advantages of the new scheme. 相似文献
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为解决XML数据更新时变更相应的子树编码导致的低效更新问题,以及插入结点过多而预留的编码空间不足造成的溢出问题,分析相关编码低效的原因,提出了一种支持XML文档更新的编码方案.采用该编码,XML文档树中现有结点的编码不受插入或删除操作的影响,避免了二次编码,降低了空间成本,采用编码对应表替代了原Dewey编码中各层之间的“.”分隔符,缩短了编码长度,并给出了基于该编码的XPath查询轴的判别方法,可快速判断结点间的结构关系.理论分析和实验结果表明了该编码方案的准确性和有效性. 相似文献
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由于XML(extensible markup language)本身是自描述的,所以XML数据流中存在大量冗余的结构信息.如何压缩XML数据流,使得在减少网络传输代价的同时有效支持压缩数据流上的查询处理,成为一个新的研究领域.目前已有的XML数据压缩技术,都需要扫描数据多遍,或者不支持数据流之上的实时查询处理.提出了一种XML数据流的压缩技术XSC(XML stream compression),实时完成XML数据流的压缩和解压缩,XSC动态构建XML元素事件序列字典并输出相关索引,能够根据XML数据流所遵从的DTD,产生XML元素事件序列图,在压缩扫描之前,产生更加合理的结构序列编码.压缩的XML数据流能够直接解压缩用于XPath的执行.实验表明,在XML数据流环境中,XSC在数据压缩率和压缩时间上要优于传统算法.同时,在压缩数据之上查询的执行代价是可以接受的. 相似文献
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提出了一种用于搜索XML文档的新的索引方法即RIST。通过采用代码化的结构序列(SES)来表示XML文档和XML查询,得出查询XML数据等同于查找子序列匹配。RIST采用树结构作为查询的基本单元,从而避免了代价高昂的连接操作。另外,RIST还在XML文档的内容和结构上提供了一个统一的索引,所以它的一个很明显的优势就是克服了仅仅根据内容或结构建立索引的弊端。实验表明RIST在支持结构查询上是一种高效的方法。 相似文献
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摘要:本文提出了一种用于搜索XML文档的新的索引方法即RIST。通过采用代码化的结构序列(SES)来表示XML文档和XML查询,我们得出查询XML数据等同于查找子序列匹配。RIST采用树结构作为查询的基本单元,从而避免了代价高昂的连接操作。另外,RIST还在XML文档的内容和结构上提供了一个统一的索引,所以它的一个很明显的优势就是克服了仅仅根据内容或结构建立索引的弊端。实验表明RIST在支持结构查询上是一种高效的方法。 相似文献