Technical Reports (CIS)

Document Type

Technical Report

Date of this Version

January 2003


University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-03-11.


This paper documents a large set of heretofore unpublished details Collins used in his parser, such that, along with Collins' thesis (Collins, 1999), this paper contains all information necessary to duplicate Collins' benchmark results. Indeed, these as-yet-unpublished details account for an 11% relative increase in error from an implementation including all details to a clean-room implementation of Collins' model. We also show a cleaner and equally-well-performing method for the handling of punctuation and conjunction, and reveal certain other probabilistic oddities about Collins' parser. We analyze not only the effect of the unpublished details, but also reanalyze the effect of certain well-known details, revealing that bilexical dependencies are barely used by the model and that head choice is not nearly as important to overall parsing performance as once thought. Finally, we perform experiments that show that the true discriminative power of lexicalization appears to lie in the fact that unlexicalized syntactic structures are generated conditioning on the head word and its part of speech.



Date Posted: 04 August 2005