XML数据压缩技术综述

随着互联网技术的迅速发展,XML已经成为Web上信息表示和数据交换的事实标准。由于XML具有自我描述能力,使得XML文档显得冗长,以至于包含了大量的冗余信息,这样必将影响数据查询处理和交换的效率。因此,XML数据压缩技术对于减少资源的使用显得特别重要。概述了XML压缩研究的现状;分析了典型的XML压缩技术,对其性能进行了比较;总结XML压缩技术的不足及发展趋势。     

可查询XML数据压缩技术概述

随着互联网技术的迅速发展,XML已经成为Web上信息表示和数据交换的事实标准。XML数据的冗余性影响了XML数据传输、查询处理等方面的效率,数据压缩是解决冗余的一种途径。介绍了典型的可查询XML压缩技术,阐述了各种压缩技术的优缺点,比较了各压缩技术的压缩率、压缩时间、支持查询的类型等;最后总结了可查询XML压缩技术的不足之处及其发展的趋势。     

网络数据交换中的XML定时数据压缩

XML即可扩展标记语言,是为了在网络中说明和交换数据而制定的标准数据格式,而作为数据载体的XML文档的体积也随着交换数据增多而变得越来越大,这给网络上的数据传输造成了很大的负担.为此,先把数据库里的数据生成XML,再加工成压缩包,就是每一条数据都是xml.zip的压缩包,利用C#编写定时程序进行定时压缩,不用手动,最后用于数据推送.     

多媒体数据压缩技术

信息时代，人们越来越多地利用计算机收集、处理多媒体数据，因此对多媒体数据压缩技术的研究也提上了日程。本文主要分析了对多媒体数据进行压缩的必要性及可行性，介绍了数据压缩的方法和对不同媒体数据进行压缩时应遵循的国际标准。最后，对不同媒体数据进行压缩时选择相应的压缩编码算法进行了讨论和分析。     

数据压缩和复原技术

本文介绍几种数据压缩和复原的方法和程序。     

一种数据压缩及还原技术

本文提出一种新的高效率压缩及还原算法－自适应数据压缩／还原算法，阐述了算法原理，实现流程及实现过程中可能遇到的问题。     

XCfde：高压缩率的XML文档压缩技术

本文提出了一种用于数据交换的XML压缩技术XCfde。XCfde采取四步压缩方案：把XML文档分离为结构数据和内容数据;自动识别数据类型并自动分类数据;对不同类型的数据采用不同的编码策略;将初步编码后的结构数据和内容数据使用7Zip进行整体压缩。XCfde拥有较高的压缩率,改善了XML数据交换的传输效率和存档中的空间利用率。     

LZW数据压缩技术及其软件实现

本文着重从图像处理方面讨论目前广泛应用的较新、较有效和复杂程序适宜的一种数据压缩技术——LZW压缩技术的算法和特点,及其软件实现方法,并给出LZW数据压缩C函数。     

XML文档压缩技术比较研究

XML已经成为互联网上信息交换和信息表示的事实标准。然而XML文档中包含大量重复出现的标签和结构等冗余信息,导致XML文档在查询处理和数据交换时付出更高的代价,特别在带宽和资源受限的设备上显得更为突出。压缩技术是解决这一问题的重要途径。搜集了近几年提出的各种XML压缩方法,从压缩率、压缩与解压时间、内存消耗、查询性能等方面比较分析了六个具有代表性的XML压缩技术,最后简要归纳了各自的优点和存在的不足,并探讨未来努力的方向。     

Effective asymmetric XML compression

The innate verbosity of the extensible markup language (XML) remains one of its main weaknesses, especially when large documents are concerned. This problem can be solved with the aid of dedicated XML compression algorithms. In this work, we describe XML word‐replacing transform (XML‐WRT), a fast and fully reversible XML transform, which, when combined with generally used LZ77‐style compression algorithms, allows to attain high compression ratios, comparable to those achieved by the current state‐of‐the‐art XML compressors. The resulting compression scheme is asymmetric in the sense that its decoder is much faster than the coder. This is a desirable practical property, as in many XML applications data are read much more often than written. The key features of the transform are dictionary‐based encoding of both document structure and content, separation of different content types into multiple streams, and dedicated encoding of specific patterns, including numbers and dates. The test results show that the proposed transform improves the XML compression efficiency of general‐purpose compressors on average by 35% in case of gzip, and 17% in case of LZMA. Compared with the current state‐of‐the‐art SCMPPM algorithm, XML‐WRT with LZMA attains over 2% better compression ratio, while being 55% faster. Copyright © 2007 John Wiley & Sons, Ltd.     

COX:高压缩率的中文XML文档压缩技术

针对当前常用的XML压缩算法没有考虑中文特点的情况,结合中文与XML的特点,提出一种高压缩率的适合中文XML文档的压缩算法COX。利用中文分词技术对XML文档进行分词处理,通过统计词频后获得排序的词典,利用Huffman编码思想对高频及长词汇进行压缩编码;解析XML文档后,把文档元素进行分类,同一类型的元素放入同一容器之中;算法还特别针对数字类型的数据进行了特殊处理。实验结果显示,相对于通用的压缩软件,COX具有更好的压缩效果,但压缩和解压缩时间要慢一些。     

XML tree structure compression using RePair

XML tree structures can conveniently be represented using ordered unranked trees. Due to the repetitiveness of XML markup these trees can be compressed effectively using dictionary-based methods, such as minimal directed acyclic graphs (DAGs) or straight-line context-free (SLCF) tree grammars. While minimal SLCF tree grammars are in general smaller than minimal DAGs, they cannot be computed in polynomial time unless P=NP$\mathsf{P}=\mathsf{NP}$. Here, we present a new linear time algorithm for computing small SLCF tree grammars, called TreeRePair, and show that it greatly outperforms the best known previous algorithm BPLEX. TreeRePair is a generalization to trees of Larsson and Moffat's RePair string compression algorithm. SLCF tree grammars can be used as efficient memory representations of trees. Using TreeRePair, we are able to produce the smallest queryable memory representation of ordered trees that we are aware of. Our investigations over a large corpus of commonly used XML documents show that tree traversals over TreeRePair grammars are 14 times slower than over pointer structures and 5 times slower than over succinct trees, while memory consumption is only 1/43 and 1/6, respectively. With respect to file compression we are able to show that a Huffman-based coding of TreeRePair grammars gives compression ratios comparable to the best known XML file compressors.     

XML compression techniques: A survey and comparison

XML has been acknowledged as the defacto standard for data representation and exchange over the World Wide Web. Being self describing grants XML its great flexibility and wide acceptance but on the other hand it is the cause of its main drawback that of being huge in size. The huge document size means that the amount of information that has to be transmitted, processed, stored, and queried is often larger than that of other data formats. Several XML compression techniques has been introduced to deal with these problems.In this paper, we provide a complete survey over the state-of-the-art of XML compression techniques. In addition, we present an extensive experimental study of the available implementations of these techniques. We report the behavior of nine XML compressors using a large corpus of XML documents which covers the different natures and scales of XML documents. In addition to assessing and comparing the performance characteristics of the evaluated XML compression tools, the study also tries to assess the effectiveness and practicality of using these tools in the real world. Finally, we provide some guidelines and recommendations which are useful for helping developers and users for making an effective decision towards selecting the most suitable XML compression tool for their needs.     

基于压缩策略的安全XML关键字查询

当含有敏感信息的XML文档在网络上传输或交换时,需要用户执行受限查询,如何提高查询效率,同时又保证敏感信息的安全一直是安全领域的研究热点。以带访问权限的实例信息树为主体,优先抽取主干信息策略,再反向作用于实例信息树存储特殊节点的压缩方法,为安全且高效的XML关键字查询奠定了基础,而且采用扩展的Dewey编码方式,为安全查询提供了方便。实验结果表明,这种基于压缩策略的安全查询方式减轻了存储负担,提高了查询效率。     

XML数据交换技术的应用与研究

针对目前存在越来越多的异构数据交换问题,本文首先介绍了基于XML在不同平台／系统之间的数据交换方面的发展趋势,分析了各种不同异构数据交换技术,最后以书费结算系统为例探讨基于XML在不同平台／系统之间异构数据交换的具体实现。     

XML函数依赖研究综述

函数依赖作为数据库规范化的基础在关系理论中起着重要的作用。近年来，XML得到广泛应用并已成为互联网上数据传输和交换的标准。由于XML半结构化的特性，使得如何定义XML函数依赖使其具有更强的描述能力，以及如何解决相应的逻辑蕴涵问题成为当今学术界所面临的挑战。针对这些问题，系统地描述了目前关于XML函数依赖的研究现状，特别是把分析的重点放在如何定义函数依赖、判断其蕴涵关系以及从XML文档中发现函数依赖等问题上。最后讨论了诸如类型化函数依赖关系等一些相关的研究方向。