Theory of Computing Systems

, Volume 57, Issue 4, pp 927–966 | Cite as

Highly Expressive Query Languages for Unordered Data Trees

  • Serge Abiteboul
  • Pierre Bourhis
  • Victor Vianu


We study highly expressive query languages for unordered data trees, using as formal vehicles Active XML and extensions of languages in the while family. All languages may be seen as adding some form of control on top of a set of basic pattern queries. The results highlight the impact and interplay of different factors: the expressive power of basic queries, the embedding of computation into data (as in Active XML), and the use of deterministic vs. nondeterministic control. All languages are Turing complete, but not necessarily query complete in the sense of Chandra and Harel. Indeed, we show that some combinations of features yield serious limitations, analogous to FO k definability in the relational context. On the other hand, the limitations come with benefits such as the existence of powerful normal forms providing opportunities for optimization. Other languages are “almost” complete, but fall short because of subtle limitations reminiscent of the copy elimination problem in object databases.


Query languages Data trees XML Expressiveness 



This work has been partially funded by the European Re-search Council under the European Community’s Seventh Framework Programme (FP7/2007-2013) / ERC grant Webdam, agreement 226513.

V. Vianu was supported in part by the NSF under award IIS-1422375. Work done in part while visiting INRIA and ENS-Cachan.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.INRIA & ENS CachanCACHAN CedexFrance
  2. 2.CNRS LIFL & Université Lille 1 & INRIA LilleVilleneuve d’AscqFrance
  3. 3.U. C. San Diego & INRIA-SaclayLa JollaUSA

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