SpanMTL: a span-based multi-table labeling for aspect-oriented fine-grained opinion extraction

Aspect-oriented Fine-grained Opinion Extraction (AFOE) aims to extract the aspect terms, corresponding opinion terms and
sentiment polarity in a target sentence. Most previous methods treat AFOE as word-level or span-level task, which ignore
the complementarity of these two tasks. To integrate the merits of word-level and span-level information, we construct an
end-to-end Span-based Multi-Table Labeling (SpanMTL) framework. SpanMTL combines word-based and span-based table
labeling to tackle AFOE task. Specifically, in the proposed model, we use two separate BiLSTMs to encode the information
of aspect and opinion terms into a word-based 2D representation table. Based on the table, we construct span-based table
with CNN by associating the word-pair representations. At last, we integrate the table label distributions of word- and spanbased table labeling to generate a multi-table labeling. The proposed method improves the performances of Opinion Pair
Extraction (OPE) and Opinion Triplet Extraction (OTE) tasks by introducing span information, especially on the datasets
with lots of spans. We have conducted various experiments on AFOE datasets to validate our method. The experimental
results show that our method outperforms other baselines when the sentences having lots of span information