@InProceedings{Kiefer_Krieger:2000,
      AUTHOR = {Kiefer, Bernd and Krieger, Hans-Ulrich},
      TITLE = {A Context-Free Approximation of Head-Driven Phrase Structure Grammar},
      YEAR = {2000},
      BOOKTITLE = {Proceedings of the 6th International Workshop on Parsing Technologies (IWPT'00), February 23-25},
      PAGES = {135-146},
      ADDRESS = {Trento, Italy},
      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.}
}