Data-efficient Active Learning for Structured Prediction with Partial Annotation and Self-Training.

In this work we propose a pragmatic method that reduces the annotation cost for structured label spaces using active learning. Our approach leverages partial annotation, which reduces labeling costs for structured outputs by selecting only the most informative substructures for annotation. We also utilize selftraining to incorporate the current model's automatic predictions as pseudo-labels for unannotated sub-structures. A key challenge in effectively combining partial annotation with self-training to reduce annotation cost is determining which sub-structures to select to label. To address this challenge we adopt an error estimator to decide the partial selection ratio adaptively according to the current model's capability. In evaluations spanning four structured prediction tasks, we show that our combination of partial annotation and self-training using an adaptive selection ratio reduces annotation cost over strong full annotation baselines under a fair comparison scheme that takes reading time into consideration.