@InCollection{Kiefer_Krieger:2002,
      AUTHOR = {Kiefer, Bernd and Krieger, Hans-Ulrich},
      TITLE = {A Context-Free Approximation of Head-Driven Phrase Structure Grammar},
      YEAR = {2002},
      BOOKTITLE = {Collaborative Language Engineering. A Case Study in Efficient Grammar-Based Processing},
      EDITOR = {Oepen, Stephan and Flickinger, Dan and Tsujii, Jun-ichi and Uszkoreit, Hans},
      ADDRESS = {Stanford},
      PUBLISHER = {CSLI Publications},
      ABSTRACT = {We present a context-free approximation of unification-based grammars, such as HPSG or PATR-II. The theoretical underpinning is established through a least fixpoint construction over a certain monotonic function. In order to reach a finite fixpoint, the concrete implementation can be parameterized in several ways, either by specifying a finite iteration depth, by using different restrictors, or by making the symbols of the CFG more complex adding annotations à la GPSG. We also present several methods that speed up the approximation process and help to limit the size of the resulting CF grammar.}
}