This paper deals with the problem of how to interrelate theory-specific treebanks and how to transform one treebank format to another. Currently, two approaches to achieve these goals can be differentiated. The first creates a mapping algorithm between treebank formats. Categories of a source format are transformed into a target format via a given set of general or language-specific mapping rules. The second relates treebanks via a transformation to a general model of linguistic categories, for example based on the EAGLES recommendations for syntactic annotations of corpora, or relying on the HPSG framework. This paper proposes a new methodology as a solution for these desiderata.