An Effective Grammar-Based Compression Algorithm for Tree Structured Data

  • Kazunori Yamagata
  • Tomoyuki Uchida
  • Takayoshi Shoudai
  • Yasuaki Nakamura
Part of the Lecture Notes in Computer Science book series (LNCS, volume 2835)


Many semistructured data such as HTML/XML files are represented by rooted trees t such that all children of each internal vertex of t are ordered and all edges of t have labels. Such data is called tree structured data. Analyzing large tree structured data is a time-consuming process in data mining. If we can reduce the size of input data without loss of information, we can speed up such a heavy process. In this paper, we consider a problem of effective compression of an ordered rooted tree, which represents given tree structured data, without loss of information. Firstly, in order to define this problem in a grammar-based compression scheme, we present a variable replacement grammar (VRG for short) over ordered rooted trees. The grammar-based compression problem for an ordered rooted tree T is defined as a problem of finding a VRG which generates only T and whose size is minimum. For the grammar-based compression problem for an ordered rooted tree, we show that there is no polynomial time algorithm with approximation ratio less than \(\frac{8593}{8592}\) unless P=NP. Secondly, based on this theoretical result, we present an effective compression algorithm for finding a VRG which generates only a given ordered rooted tree and whose size is as small as possible. Finally, in order to evaluate the performance of our grammar-based compression algorithm, we report some experimental results.


Compression Ratio Rooted Tree Term Tree Compression Algorithm Graph Transformation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2003

Authors and Affiliations

  • Kazunori Yamagata
    • 1
  • Tomoyuki Uchida
    • 1
  • Takayoshi Shoudai
    • 2
  • Yasuaki Nakamura
    • 1
  1. 1.Faculty of Information SciencesHiroshima City UniversityHiroshimaJapan
  2. 2.Department of InformaticsKyushu UniversityKasugaJapan

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