Most answer sentence ranking algorithms operate under the assumption that the degree of syntactic and/or semantic similarity between questions and answer sentences is a sufficiently strong predictor of answer sentence relevance (Wang et al., 2007;Yih et al., 2013;Yu et al., 2014;Severyn and Moschitti, 2015).
answer extraction algorithms frequently assess candidate answer phrases based primarily on their own properties relative to the question (e.g., whether the question is a who question and the phrase refers to a person), making inadequate or no use of sentence-level evidence (Yao et al., 2013a;Severyn and Moschitti, 2013).