Czech Technical University
In this paper, the authors give an overview of XML formal models, summarizes database engineering practices, problems and their evolution. They focus on categorical aspects of XML formal models. Many formal models such as XML data model, XQuery data model or Algebra for XML can be described in terms of category theory. This kind of description allows to consider generic properties of these formalisms, e.g. expressive power, optimization, reduction or translation between them, among others. These properties are rather crucial to comparison of different XML formal models and to consequent decision which formal system should be used to solve a concrete problem.