Note that, based on H2 and H3, paraphrase Q-Q and T-T can be directly extracted from raw Q-T pairs.
in consideration of precision, we extract them from paraphrase Q-T. We call our paraphrase Q-Q and T-T extraction approach as a pivot approach, since we use titles as pivots (queries as targets) when extracting paraphrase Q-Q and use queries as pivots (titles as targets) when extracting paraphrase T-T. Our paraphrase extraction algorithm is shown in Table 2.