Learning Semantic Role Labeling from Compatible Label Sequences.

This paper addresses the question of how to efficiently learn from disjoint, compatible label sequences. We argue that the compatible structures between disjoint label sets help model learning and inference. We verify this hypothesis on the task of semantic role labeling (SRL), specifically, tagging a sentence with two role sequences: VerbNet arguments and PropBank arguments. Prior work has shown that cross-task interaction improves performance. However, the two tasks are still separately decoded, running the risk of generating structurally inconsistent label sequences (as per lexicons like SEMLINK). To eliminate this issue, we first propose a simple and effective setup that jointly handles VerbNet and PropBank labels as one sequence. With this setup, we show that enforcing SEMLINK constraints during decoding constantly improves the overall F1. With special input constructions, our joint model infers VerbNet arguments from PropBank arguments with over 99% accuracy. We also propose a constrained marginal model that uses SEMLINK information during training to further benefit from the large amounts of PropBank-only data. Our models achieve state-of-the-art F1's on VerbNet and PropBank argument labeling on the CoNLL05 dataset with strong out-of-domain generalization.