Which Side are You on? Identifying Perspectives at the Document and Sentence Levels

Proceedings of the 10th Conference on Computational Natural Language Learning (CoNLL-X), pages 109–116, New York City, June 2006. c⃝2006 Association for Computational Linguistics Which Side are You on? Identifying Perspectives at the Document and Sentence Levels Wei-Hao Lin Language Technologies Institute Carnegie Mellon University Pittsburgh, PA 15213 whlin@cs.cmu.edu Theresa Wilson, Janyce Wiebe Intelligent Systems Program University of Pittsburgh Pittsburgh, PA 15260 {twilson,wiebe}@cs.pitt.edu Alexander Hauptmann School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213 alex@cs.cmu.edu Abstract In this paper we investigate a new problem of identifying the perspective from which a document is written. By perspective we mean a point of view, for example, from the perspective of Democrats or Repub- licans. Can computers learn to identify the perspective of a document? Not every sentence is written strongly from a per- spective. Can computers learn to identify which sentences strongly convey a partic- ular perspective? We develop statistical models to capture how perspectives are expressed at the document and sentence levels, and evaluate the proposed mod- els on articles about the Israeli-Palestinian conflict. The results show that the pro- posed models successfully learn how per- spectives are reflected in word usage and can identify the perspective of a document with high accuracy. 1 Introduction In this paper we investigate a new problem of au- tomatically identifying the perspective from which a document is written. By perspective we mean a “subjective evaluation of relative significance, a point-of-view.”1 For example, documents about the Palestinian-Israeli conflict may appear to be about the same topic but reveal different perspectives: 1The American Heritage Dictionary of the English Lan- guage, 4th ed. (1) The inadvertent killing by Israeli forces of Palestinian civilians – usually in the course of shooting at Palestinian terrorists – is considered no different at the moral and ethical level than the deliberate targeting of Israeli civilians by Palestinian suicide bombers. (2) In the first weeks of the Intifada, for example, Palestinian public protests and civilian demonstrations were answered brutally by Israel, which killed tens of unarmed protesters. Example 1 is written from an Israeli perspective; Example 2 is written from a Palestinian perspec- tive. Anyone knowledgeable about the issues of the Israeli-Palestinian conflict can easily identify the perspectives from which the above examples were written. However, can computers learn to identify the perspective of a document given a training cor- pus? When an issue is discussed from different per- spectives, not every sentence strongly reflects the perspective of the author. For example, the follow- ing sentences were written by a Palestinian and an Israeli. (3) The Rhodes agreements of 1949 set them as the ceasefire lines between Israel and the Arab states. (4) The green line was drawn up at the Rhodes Armistice talks in 1948-49. Examples 3 and 4 both factually introduce the back- ground of the issue of the “green line” without ex- pressing explicit perspectives. Can we develop a 109 system to automatically discriminate between sen- tences that strongly indicate a perspective and sen- tences that only reflect shared …

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