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Making Neural QA as Simple as Possible but not Simpler

Paper · 2017 · Dirk Weissenborn, Georg Wiese and Laura Seiffe

Summary

Large extractive QA datasets such as SQuAD and NewsQA prompted many neural reading models. These models grew steadily more elaborate, especially in their layers for word-by-word interaction between question and context, yet they were seldom compared against a strong simple baseline. Weissenborn, Wiese and Seiffe build such baselines from an intuitive context/type matching heuristic: a correct span should have the answer type the question implies and should appear near many question words.

They first build a bag-of-words model that follows this rule almost literally. They then introduce FastQA, which passes context embeddings and two word-in-question features (one binary, one embedding-weighted) through a single BiRNN and predicts answer start and end separately. FastQA has no dedicated interaction layer, yet it performs competitively against much more complex systems. Adding an interaction layer (FastQAExt) yields only small, unsystematic gains at a clear cost in speed and memory.

The study suggests that two ingredients are enough for strong performance: awareness of question words and a composition function richer than bag-of-words. This reframes both earlier architectural complexity and how hard these benchmarks really are.

Key points

  • BoW baseline design: The bag-of-words model scores candidate spans of up to 10 words. Its type score compares a span representation with the lexical answer type (LAT). Its context score combines 12 weighted word-in-question averages, taken over 5-, 10- and 20-token windows on each side of the span.
  • FastQA architecture: Embeddings combine word vectors with a character CNN (filter width 5, max-pooling). A projection and highway layer follow, then a BiRNN that receives the wiq-b and wiq-w features as extra inputs.
  • Efficiency: FastQA runs about twice as fast as FastQAExt and DCN. It needs roughly 2–4× less memory than those two models.
  • FastQA vs. FastQAExt on SQuAD dev: FastQAExt alone answered 589 questions correctly, against 415 for FastQA alone. The authors found no systematic difference between these two sets in question type, length or required reasoning.
  • Error analysis: About 64% of the 55 inspected errors (35) stem directly from applying the heuristic. About 88% of 50 correct answers (44) are also explained by it. Remaining weaknesses include fine-grained answer types, coreference, abbreviations and nested syntax.

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

 Fields, topics and concepts

Cite

Cite as Dirk Weissenborn, Georg Wiese and Laura Seiffe. 2017. Making Neural QA as Simple as Possible but not Simpler. arXiv:1703.04816.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.1703.04816 · arXiv 1703.04816

@misc{weissenborn2017making,
  title = {{Making Neural QA as Simple as Possible but not Simpler}},
  author = {Dirk Weissenborn, Georg Wiese and Laura Seiffe},
  year = {2017},
  doi = {10.48550/arxiv.1703.04816},
  eprint = {1703.04816},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.1703.04816}
}

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