What is the Jeopardy Model? A Quasi-Synchronous Grammar for QA
Summary
The paper addresses answer-sentence selection for short-answer (factoid) questions: choosing, from candidates returned by retrieval, the sentence that actually answers a question. Bag-of-words matching struggles with lexical substitutions (leader vs. president) and syntactic shifts (leader of France vs. French president). The authors therefore treat the question as if it were generated from the answer sentence through loose syntactic and semantic transformations. They implement this as the "Jeopardy model," a probabilistic quasi-synchronous dependency grammar adapted from D. Smith and Eisner's (2006) machine translation work. The model mixes a robust non-lexical syntax/alignment component with an optional log-linear component that uses WordNet features. Word alignments between the dependency trees are hidden and summed out, and the model is trained with conditional maximum likelihood. On TREC QA data, it clearly beats reimplemented versions of two prior systems, Cui et al. (2005) and Punyakanok et al. (2004), even when WordNet is added to those baselines. The work shows that explicitly modeling soft tree-to-tree transformations helps QA, where earlier attempts to add syntactic features had often failed.
Key points
- Task setup:
- Candidate answers are fixed at sentence granularity.
- Dependency parses come from a McDonald et al. parser.
- The prior p(a) over candidates is assumed uniform.
- Training uses manually judged answers for TREC 8–12 questions 1–100.
- Main result (test set):
- The full Jeopardy model reaches MAP 0.6029 and MRR 0.6852.
- The best baseline, Cui et al., gets MAP 0.4350 and MRR 0.5569.
- The Jeopardy base model alone (without the lexical-semantics component) gets MAP 0.4828 and MRR 0.5571.
- Baselines:
- TreeMatch is a reimplementation of Punyakanok et al. (2004), based on tree edit distance and requiring no training.
- Cui et al. (2005) relies on dependency-path similarity.
- Both were also extended with WordNet ("+WN").
- Noisy training data:
- Questions 101–2,393 were labeled automatically. A candidate counted as correct if it shared at least three non-stop word types with the question and matched the answer pattern.
- This hurt every trained method. The Jeopardy model degraded less (test MAP 0.5655) than Cui et al. (0.2833; 0.3811 with +WN).
- Summing vs. maximizing over alignments:
- Summing in both training and decoding works best (test MAP 0.6029).
- Using the max during training is worse (0.5559–0.5571).
- Significance was tested with a two-tailed paired t-test (p < 0.03).
Interesting ideas
- I1. Reversed generative story: Imagine the question being produced from the answer, as a noisy-channel "translation." This makes scoring a QA pair a tree-to-tree alignment problem. The same framing could apply to paraphrase detection, textual entailment, or matching queries to documents.
- I2. Loose grammar instead of strict synchronous structure: Quasi-synchronous grammar lets one tree be generated by a grammar inspired by the other tree. It allows a menu of local alignment configurations instead of demanding isomorphism. This suits "free" correspondences such as morphologically rich or loosely translated text.
- I3. Alignment as a latent variable that is summed out: The model never commits to one word correspondence. It marginalizes over all of them, and the experiments show this beats picking the single best alignment, especially during training. This is useful wherever alignments are uncertain and gold alignments are unavailable.
- I4. Mixing a smoothed base model with an optional log-linear component: The multinomial base model provides robustness and smoothing. The log-linear part can absorb arbitrary task-specific features (e.g., WordNet relations) without normalizing over huge sets. The pattern suits low-resource settings, where lexical resources may be sparse but still helpful.
- I5. Cheap noisy labeling as a stress test: Automatically labeled data (keyword overlap plus answer pattern) is used both to expand training and to measure how gracefully each method degrades under label noise. This is a reusable evaluation trick when manual annotation is expensive.
Cited by
- Universal Conceptual Cognitive Annotation (UCCA)
- Paraphrase Identification as Probabilistic Quasi-Synchronous Recognition
- Feature-Rich Translation by Quasi-Synchronous Lattice Parsing
- Tree Edit Models for Recognizing Textual Entailments, Paraphrases, and Answers to Questions
- How Much Reading Does Reading Comprehension Require? A Critical Investigation of Popular Benchmarks
- Know What You Don't Know: Unanswerable Questions for SQuAD
- Bilateral Multi-Perspective Matching for Natural Language Sentences
- Learning to Simplify Sentences with Quasi-Synchronous Grammar and Integer Programming
- WikiQA: A Challenge Dataset for Open-Domain Question Answering
- ABCNN: Attention-Based Convolutional Neural Network for Modeling Sentence Pairs
Cite
@inproceedings{wang2007what,
title = {{What is the Jeopardy Model? A Quasi-Synchronous Grammar for QA}},
author = {Wang, Mengqiu and Smith, Noah A. and Mitamura, Teruko},
booktitle = {Proceedings of the 2007 Joint Conference on Empirical Methods in Natural Language Processing and Computational Natural Language Learning (EMNLP-CoNLL)},
year = {2007},
url = {https://aclanthology.org/D07-1003/}
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