  Event grounding aims at linking mention references in text corpora to events
from a knowledge base (KB). Previous work on this task focused primarily on
linking to a single KB event, thereby overlooking the hierarchical aspects of
events. Events in documents are typically described at various levels of
spatio-temporal granularity (Glavas et al. 2014). These hierarchical relations
are utilized in downstream tasks of narrative understanding and schema
construction. In this work, we present an extension to the event grounding task
that requires tackling hierarchical event structures from the KB. Our proposed
task involves linking a mention reference to a set of event labels from a
subevent hierarchy in the KB. We propose a retrieval methodology that leverages
event hierarchy through an auxiliary hierarchical loss (Murty et al. 2018). On
an automatically created multilingual dataset from Wikipedia and Wikidata, our
experiments demonstrate the effectiveness of the hierarchical loss against
retrieve and re-rank baselines (Wu et al. 2020; Pratapa, Gupta, and Mitamura
2022). Furthermore, we demonstrate the systems' ability to aid hierarchical
discovery among unseen events.
