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Identifying Sources of Opinions with Conditional Random Fields and Extraction Patterns

Paper · 2005 · Yejin Choi, Claire Cardie, Ellen Riloff et al.

Summary

The paper addresses automatically finding the source of an opinion: the person or entity holding or expressing a sentiment, belief or emotion in text. This includes both first-hand (direct) holders and second-hand (indirect) ones whose view is reported through someone else. The authors treat this as an information extraction problem and build a hybrid system with two parts:

  • A linear-chain Conditional Random Field that labels tokens as source start, source continuation, or outside. It uses capitalization, part-of-speech, opinion-lexicon, dependency-parse and semantic-class features.
  • AutoSlog-SE, a new fully automatic version of AutoSlog. It learns extraction patterns whose matches become extra CRF features.

Automatic induction of feature conjunctions is applied on top. Evaluated on the NRRC corpus, which carries MPQA-style annotations of direct and indirect sources, the combination beats either component alone. It reaches 81.2% precision and 60.6% recall under an overlap measure, and 79.3% precision and 59.5% recall under head-noun matching. This matters for opinion-oriented question answering and summarization, which must tell apart whose opinion is whose.

Key points

  • Tagging scheme: three labels, 'S' (first token of a source), 'T' (continuation) and '-' (outside), equivalent to IOB chunk tagging.

  • Feature sources: GATE supplies coarse POS tags in a ±2 window, the Collins (1999) dependency parser provides structural features, and the Sundance shallow parser yields 7 binary semantic-class features (authority, government, human, media, organization/company, proper name, other).

  • Opinion lexicon: it starts from roughly 500 words from Wiebe et al. (2002). It is extended with content words from the training data that appear inside opinion annotations at least 50% of the time.

  • Final results (basic features, IE-pattern features and feature induction combined):

    MeasureF-measurePrecisionRecall
    Overlap (OL)69.481.2%60.6%
    Head-noun matching (HM)68.079.3%59.5%
    Exact match (EM)62.072.7%54.1%
  • Error analysis: the main causes were sentence-splitting errors in GATE that made the parser fail, complex syntax, missed negation, and idiomatic opinion phrases absent from the lexicon.

Interesting ideas

  • I1. Patterns as features. Instead of running a pattern learner and a statistical tagger separately, the learned extraction patterns are fed into the CRF as features. This lets a symbolic, interpretable component and a probabilistic one be combined in other extraction tasks without hand-tuning how they interact.
  • I2. Phrase-level lexicon propagation. An opinion word marks its whole syntactic chunk as opinion-bearing, so a single-word lexicon can cover multi-word expressions. This is a cheap way to stretch any word-level lexicon to phrases.
  • I3. Data-driven lexicon expansion. Content words that mostly occur inside annotated spans in the training data are added to the lexicon. The same heuristic could grow domain lexicons wherever span annotations exist.
  • I4. Explicit conjunction features. Log-linear models cannot combine features on their own, so automatic induction of conjunctive features (e.g., human entity plus a parent chunk containing an opinion) gave consistent gains. This is worth trying for any CRF or logistic model with many sparse cues.
  • I5. Multiple evaluation measures. Reporting overlap, head-noun and exact-match scores shows how much error comes from span boundaries versus wrong entities. This is useful for any span-extraction evaluation.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

Cite

Cite as Yejin Choi, Claire Cardie, Ellen Riloff and Siddharth Patwardhan. 2005. Identifying Sources of Opinions with Conditional Random Fields and Extraction Patterns. Proceedings of Human Language Technology Conference and Conference on Empirical Methods in Natural Language Processing.

The paper itself, not this page. BibTeX from the library's record of the work.

@inproceedings{choi2005identifying,
  title = {{Identifying Sources of Opinions with Conditional Random Fields and Extraction Patterns}},
  author = {Yejin Choi, Claire Cardie, Ellen Riloff and Siddharth Patwardhan},
  booktitle = {Proceedings of Human Language Technology Conference and Conference on Empirical Methods in Natural Language Processing},
  year = {2005},
  doi = {10.3115/1220575.1220620},
  url = {https://doi.org/10.3115/1220575.1220620}
}

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