The Penn Treebank: Annotating Predicate Argument Structure

THE PENN TREEBANK: ANNOTATING PREDICATE ARGUMENT STRUCTURE Mitchell Marcus, Grace Kim, Mary Ann Marcinkiewicz, Robert MacIntyre, Ann Bies, Mark Ferguson, Karen Katz, Britta Schasberger Department of Computer and Information Science University of Pennsylvania Philadelphia, PA, USA ABSTRACT The Penn Treebank has recently implemented a new syn- tactic annotation scheme, designed to highlight aspects of predicate-argument structure. This paper discusses the implementation of crucial aspects of this new annotation scheme. It incorporates a more consistent treatment of a wide range of grammatical phenomena, provides a set of coin- dexed null elements in what can be thought of as "underly- ing" position for phenomena such as wh-movement, passive, and the subjects of infinitival constructions, provides some non-context free annotational mechanism to allow the struc- ture of discontinuous constituents to be easily recovered, and allows for a clear, concise tagging system for some semantic roles. 1. INTRODUCTION During the first phase of the The Penn Treebank project [10], ending in December 1992, 4.5 million words of text were tagged for part-of-speech, with about two-thirds of this ma- terial also annotated with a skeletal syntactic bracketing. All of this material has been hand corrected after processing by automatic tools. The largest component of the corpus con- sists of materials from the Dow-Jones News Service; over 1.6 million words of this material has been hand parsed, with an additional 1 million words tagged for part of speech. Also included is a skeletally parsed version of the Brown corpus, the classic million word balanced corpus of American English [5, 6]. hand-retagged using the Penn Treebank tagset. The level of syntactic analysis annotated during this phase of this project was an extended and somewhat modified form of the skeletal analysis which has been produced by the tree- banking effort in Lancaster, England [7]. The released mate- rials in the current Penn Treebank, although still in very pre- liminary form, have been widely distributed, both directly by us, on the ACL/DCI CD-ROM, and now on CD-ROM by the Linguistic Data Consortium; it has been used for purposes ranging from serving as a gold-standard for parser testing to serving as a basis for the induction of stochastic grammars to serving as a basis for quick lexicon induction. Many users of the Penn Treebank now want forms of an- notation richer than provided by the project's first phase, as well as an increase in the consistency of the preliminary corpus. Some would also like a less skeletal form of anno- tation, expanding the essentially context-free analysis of the current treebank to indicate non-contiguous structures and dependencies. Most crucially, there is a strong sense that the Treebank could be of much more use if it explicitly provided some form of predicate-argument structure. The desired level of representation would make explicit at least the logical sub- ject and logical object of the verb, and indicate, at least in clear cases, how subconstituents are semantically related to their predicates. Such a representation could serve as both a starting point for the kinds of …

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