Explore Coarse-Grained Structures for Syntactically Controllable Paraphrase Generation.

Syntactically controlled paraphrase generation can produce diverse paraphrases by exposing syntactic control, where both semantic preservation and syntactic variations are two important factors. Previous works mainly focus on using fine-grained syntactic structures (e.g., full parse tree) as syntactic control. While these methods can achieve excellent syntactic controllability, leads to failing to preserve the semantics of the input sentence. The main reason is that it is difficult to retrieve perfectly compatible syntactic structures with the input sentences. In this paper, we explore coarse-grained syntactic structures to trade-off semantic preservation and syntactic variations. Furthermore, to improve semantic preservation and syntactic controllability, we propose a Syntax Attention-Guided Paraphrase (SAGP) model that can correctly select syntactic information according to the current state for surface realization. Experiment results show that SAGP outperforms the previous state-of-the-art method under the same setting. Additionally, we validate that using coarse-grained structures can generate more semantically reasonable text without affecting the syntactic controllability.