  In this paper, we study the identity of textual events from different
documents. While the complex nature of event identity is previously studied
(Hovy et al., 2013), the case of events across documents is unclear. Prior work
on cross-document event coreference has two main drawbacks. First, they
restrict the annotations to a limited set of event types. Second, they
insufficiently tackle the concept of event identity. Such annotation setup
reduces the pool of event mentions and prevents one from considering the
possibility of quasi-identity relations. We propose a dense annotation approach
for cross-document event coreference, comprising a rich source of event
mentions and a dense annotation effort between related document pairs. To this
end, we design a new annotation workflow with careful quality control and an
easy-to-use annotation interface. In addition to the links, we further collect
overlapping event contexts, including time, location, and participants, to shed
some light on the relation between identity decisions and context. We present
an open-access dataset for cross-document event coreference, CDEC-WN, collected
from English Wikinews and open-source our annotation toolkit to encourage
further research on cross-document tasks.
