An annotation similarity model in passage ranking for historical fact validation

State-of-the-art question answering (QA) systems employ passage retrieval based on bag-of-words similarity models with respect to a query and a passage. We propose a combination of a traditional bag-of-words similarity model and an annotation similarity model to improve passage ranking. The proposed annotation similarity model is generic enough to process annotations of arbitrary types. Historical fact validation is a subtask to determine whether a given sentence tells us historically correct information, which is important for a QA task on world history. Experimental results show that the combined model gains up to 7.7% and 4.2% improvements in historical fact validation in terms of precision at rank 1 and mean reciprocal rank, respectively.