SPECTRA: Sparse Structured Text Rationalization

Nuno M. Guerreiro, André F. T. Martins


Abstract
Selective rationalization aims to produce decisions along with rationales (e.g., text highlights or word alignments between two sentences). Commonly, rationales are modeled as stochastic binary masks, requiring sampling-based gradient estimators, which complicates training and requires careful hyperparameter tuning. Sparse attention mechanisms are a deterministic alternative, but they lack a way to regularize the rationale extraction (e.g., to control the sparsity of a text highlight or the number of alignments). In this paper, we present a unified framework for deterministic extraction of structured explanations via constrained inference on a factor graph, forming a differentiable layer. Our approach greatly eases training and rationale regularization, generally outperforming previous work on what comes to performance and plausibility of the extracted rationales. We further provide a comparative study of stochastic and deterministic methods for rationale extraction for classification and natural language inference tasks, jointly assessing their predictive power, quality of the explanations, and model variability.
Anthology ID:
2021.emnlp-main.525
Volume:
Proceedings of the 2021 Conference on Empirical Methods in Natural Language Processing
Month:
November
Year:
2021
Address:
Online and Punta Cana, Dominican Republic
Editors:
Marie-Francine Moens, Xuanjing Huang, Lucia Specia, Scott Wen-tau Yih
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
6534–6550
Language:
URL:
https://aclanthology.org/2021.emnlp-main.525
DOI:
10.18653/v1/2021.emnlp-main.525
Bibkey:
Cite (ACL):
Nuno M. Guerreiro and André F. T. Martins. 2021. SPECTRA: Sparse Structured Text Rationalization. In Proceedings of the 2021 Conference on Empirical Methods in Natural Language Processing, pages 6534–6550, Online and Punta Cana, Dominican Republic. Association for Computational Linguistics.
Cite (Informal):
SPECTRA: Sparse Structured Text Rationalization (Guerreiro & Martins, EMNLP 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.emnlp-main.525.pdf
Video:
 https://aclanthology.org/2021.emnlp-main.525.mp4
Code
 deep-spin/spectra-rationalization +  additional community code
Data
IMDb Movie ReviewsSNLISST