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DOI: 10.4230/LIPIcs.ICDT.2017.18

Compression of Unordered XML Trees

Authors: Markus Lohrey, Sebastian Maneth, and Carl Philipp Reh

Published in: LIPIcs, Volume 68, 20th International Conference on Database Theory (ICDT 2017)

Abstract

Many XML documents are data-centric and do not make use of the inherent document order. Can we provide stronger compression for such documents through giving up order? We first consider compression via minimal dags (directed acyclic graphs) and study the worst case ratio of the size of the ordered dag divided by the size of the unordered dag, where the worst case is taken for all trees of size n. We prove that this worst case ratio is n / log n for the edge size and n log log n / log n for the node size. In experiments we compare several known compressors on the original document tree versus on a canonical version obtained by length-lexicographical sorting of subtrees. For some documents this difference is surprisingly large: reverse binary dags can be smaller by a factor of 3.7 and other compressors can be smaller by factors of up to 190.

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Markus Lohrey, Sebastian Maneth, and Carl Philipp Reh. Compression of Unordered XML Trees. In 20th International Conference on Database Theory (ICDT 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 68, pp. 18:1-18:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{lohrey_et_al:LIPIcs.ICDT.2017.18,
  author =	{Lohrey, Markus and Maneth, Sebastian and Reh, Carl Philipp},
  title =	{{Compression of Unordered XML Trees}},
  booktitle =	{20th International Conference on Database Theory (ICDT 2017)},
  pages =	{18:1--18:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-024-8},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{68},
  editor =	{Benedikt, Michael and Orsi, Giorgio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2017.18},
  URN =		{urn:nbn:de:0030-drops-70584},
  doi =		{10.4230/LIPIcs.ICDT.2017.18},
  annote =	{Keywords: tree compression, directed acyclic graphs, XML}
}

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Compression of Unordered XML Trees

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