Transformation of data documents is of special importance to use XML as the universal data interchange format on the Web. Data transformation is used in many tasks that require data to be transferred between existing, independently created Web-oriented applications. To perform such transformation one can use W3C’s XSLT or XQuery. But these languages are devoted to detailed programming of transformation procedures. In this paper we show how data transformation can by specify by means of high-level rule specifications based on uniform unranked tree transducers. We show that our approach is both descriptive and expressive, and we illustrate how it can be used to specify and perform transformations of XML documents.