1 Determining the Hierarchical Structure of Perspective and Speech Expressions Eric Breck and Claire Cardie Cornell University Department of Computer Science
Cornell University Computer Science COLING Events in the News
Cornell University Computer Science COLING Reporting events
Cornell University Computer Science COLING Reporting in text Clapp sums up the environmental movement’s reaction: “The polluters are unreasonable’’ Charlie was angry at Alice’s claim that Bob was unhappy
Cornell University Computer Science COLING Perspective and Speech Expressions (pse’s) A perspective expression is text denoting an explicit opinion, belief, sentiment, etc. The actor was elated that … John’s firm belief in … A speech expression is text denoting spoken or written communication … argued the attorney... … the 9/11 Commission’s final report …
Cornell University Computer Science COLING Grand Vision angryclaim (implicit) unhappy Charlie was angry at Alice’s claim that Bob was unhappy writer CharlieAlice Bob that Bob was unhappy
Cornell University Computer Science COLING This Work angryclaim (implicit) unhappy
Cornell University Computer Science COLING System Output: Pse Hierarchy Charlie was angry at Alice’s claim that Bob was unhappy 78% accurate! angryclaim (implicit) unhappy
Cornell University Computer Science COLING Related Work: Abstract Bergler, 1993 Lexical semantics of reporting verbs Gerard, 2000 Abstract model of news reader
Cornell University Computer Science COLING Related Work: Concrete Bethard et al., 2004 Extract propositional opinions & holders Wiebe, 1994 Tracks “point of view” in narrative text Wiebe et al., 2003 Preliminary results on pse identification Gildea and Jurafsky, 2002 Semantic Role ID - use for finding sources?
Cornell University Computer Science COLING Baseline 1: Only filter through writer Only 66% correct angryclaim (implicit) unhappy
Cornell University Computer Science COLING Baseline 2: Dependency Tree 72% correct angry (implicit) claim unhappy claim unhappy claim unhappy
Cornell University Computer Science COLING A Learning Approach How do we cast the recovery of hierarchical structure as a learning problem? Simplest solution Learn pairwise attachment decisions Is pse parent the parent of pse target ? Combine decisions to form tree Other solutions are possible (n-ary decisions, tree-modeling, etc.)
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Training instances angryclaim (implicit) unhappy
Cornell University Computer Science COLING Decision Combination (implicit) angry claim unhappy
Cornell University Computer Science COLING Decision Combination angry (implicit) angry claim unhappy
Cornell University Computer Science COLING Decision Combination angry (implicit) claim unhappy
Cornell University Computer Science COLING Decision Combination angry claim (implicit) claim unhappy
Cornell University Computer Science COLING Decision Combination angryclaim (implicit) unhappy
Cornell University Computer Science COLING Decision Combination angryclaim (implicit) unhappy
Cornell University Computer Science COLING Decision Combination angryclaim (implicit) unhappy
Cornell University Computer Science COLING Features(1) All features based on error analysis Parse-based features Domination+ variants Positional features Relative position of pse parent and pse target
Cornell University Computer Science COLING Features(2) Lexical features writer’s implicit pse “said” “according to” part of speech Genre-specific features Charlie, she noted, dislikes Chinese food. “Alice disagrees with me,” Bob said.
Cornell University Computer Science COLING Resources GATE toolkit (Cunningham et al, 2002) - part-of-speech, tokenization, sentence boundaries Collins parser (1999) - extracted dependency parses CASS partial parser (Abney, 1997) IND decision trees (Buntine, 1993)
Cornell University Computer Science COLING Data From the NRRC Multi-Perspective Question Answering workshop (Wiebe, 2002) 535 newswire documents (66 for development, 469 for evaluation) All pse’s annotated, along with sources and other information Hierarchical pse structure annotated for each sentence*
Cornell University Computer Science COLING Example (truncated) model One learned tree, truncated to depth 3: pse 0 is parent of pse 1 iff pse 0 is (implicit) And pse 1 is not in quotes OR pse 0 is said Typical trees on development data: Depth ~20, ~700 leaves
Cornell University Computer Science COLING Evaluation Dependency-based metric (Lin, 1995) Percentage of pse’s whose parents are identified correctly Percentage of sentences with perfectly identified structure Performance of binary classifier
Cornell University Computer Science COLING Results
Cornell University Computer Science COLING Error Analysis Pairwise decisions prevent the model from learning larger structure Speech events and perspective expressions behave differently Treebank-style parses don’t always have the structure we need
Cornell University Computer Science COLING Future Work Identify pse’s Identify sources Evaluate alternative structure-learning methods Use the structure to generate perspective-oriented summaries
Cornell University Computer Science COLING Conclusions Understanding pse structure is important for understanding text Automated analysis of pse structure is possible
Cornell University Computer Science COLING Thank you!