Acknowledgements

I wish to thank William Cohen, Eibe Frank, Alexandros Kalousis, Stefan Kramer, Rich Maclin, Dragos Margineantu, Johann Petrak, Foster Provost, Lupco Todorovski, Gerhard Widmer, and the maintainers of and contributors to the UCI collection of databases for discussions, programs, databases, and/or pointers to relevant literature. Thanks are also due to the anonymous reviewers and the editor, in particular for the careful comments on the theoretical section of this paper.

The Austrian Research Institute for Artificial Intelligence is supported by the Austrian Federal Ministry of Education, Science and Culture. The author is supported by the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung (FWF) under grant no. P12645-INF.