Towards algebraic query optimisation for XQuery

  • Authors:

  • Markus Kirchberg;Faizal Riaz-ud-Din;Klaus-Dieter Schewe;Alexei Tretiakov

  • Affiliations:

  • Department of Information Systems and, Information Science Research Centre, Massey University, Palmerston North, New Zealand;Department of Information Systems and, Information Science Research Centre, Massey University, Palmerston North, New Zealand;Department of Information Systems and, Information Science Research Centre, Massey University, Palmerston North, New Zealand;Department of Information Systems and, Information Science Research Centre, Massey University, Palmerston North, New Zealand

  • Venue:
  • Journal on Data Semantics VII
  • Year:
  • 2005

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Abstract

XML-based databases have become a major area of interest in database research. Abstractly speaking they can be considered as a resurrection of complex-value databases using constructors for records, lists, unions plus optionality and references. XQuery has become the standard query language for XML. As XQuery is a declarative query language, the problem of query optimisation arises. In this paper an algebraic approach to query optimisation is introduced. This is based on a translation of XQuery into a query algebra for rational tree types. The algebra uses simple operations on types and structural recursion for lists. The translation exploits linguistic reflection for the type-safe expansion of path expressions. The availability of an algebraic representation of queries permits query rewriting, which in combination with cost heuristics permits queries to be rewritten and thus optimised.