Beyond language modeling, methods for PCFG induction from treebanks have been a popular topic in the field over the past decade, and some understanding of the impact of flattening trees can be had in <cite>Johnson (1998)</cite> , where the beneficial impact of various tree transformations for probabilistic grammars is presented. None of this work is discussed or cited, and the naive reader might be left with the impression that data-driven approaches have been demonstrated to underperform relative to knowledge-based approaches, when in fact the authors simply demonstrate that their hybrid grammar-based/data-driven approach outperforms class-based language models. Perhaps this is worth demonstrating, but the chapter couches the results within the context of a clash between paradigms, which simply does not ring true. This one misstep, however, does not detract from the quality of the authors' system, nor from the interesting presentation of too-often-ignored aspects of spoken language systems engineering. The book and the toolkit it describes can serve a very useful pedagogical purpose by providing a foundation upon which students and researchers