UCD-CS at W-NUT 2020 Shared Task-3: A Text to Text Approach for COVID-19 Event Extraction on Social Media

In this paper, we describe our approach in the shared task: COVID-19 event extraction from Twitter. The objective of this task is to extract answers from COVID-related tweets to a set of predefined slot-filling questions. Our approach treats the event extraction task as a question answering task by leveraging the transformer-based T5 text-to-text model. According to the official exact match based evaluation scores returned, namely F1, our submitted run can achieve competitive performance as compared to other participating runs (Top 3). However, we argue that this evaluation can potentially underestimate the actual performance of runs based on text-generation approaches (e.g. our run). This is due to the fact that although some predictions of such runs answer the slot questions well, they may not be an exact string match for the gold standard answers. To further measure the extent of this underestimation, we adopt a simple exact answer transformation method aiming at converting the well-answered predictions to exactly-matched predictions. The results show that after the transformation our run reaches the same level of performance as the best participating run. Our code is publicly available to aid reproducibility.