Relevance-guided Supervision for OpenQA with ColBERT
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Systems for Open-Domain Question Answering (OpenQA) generally depend on a retriever for finding candidate passages in a large corpus and a reader for extracting answers from those passages. In much recent work, the retriever is a learned component that uses coarse-grained vector representations of questions and passages. We argue that this modeling choice is insufficiently expressive for dealing with the complexity of natural language questions. To address this, we define ColBERT-QA, which adapts the scalable neural retrieval model ColBERT to OpenQA. ColBERT creates fine-grained interactions between questions and passages. We propose a weak supervision strategy that iteratively uses ColBERT to create its own training data. This greatly improves OpenQA retrieval on both Natural Questions and TriviaQA, and the resulting end-to-end OpenQA system attains state-of-the-art performance on both of those datasets.
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