  Almost all statements in knowledge bases have a temporal scope during which
they are valid. Hence, knowledge base completion (KBC) on temporal knowledge
bases (TKB), where each statement \textit{may} be associated with a temporal
scope, has attracted growing attention. Prior works assume that each statement
in a TKB \textit{must} be associated with a temporal scope. This ignores the
fact that the scoping information is commonly missing in a KB. Thus prior work
is typically incapable of handling generic use cases where a TKB is composed of
temporal statements with/without a known temporal scope. In order to address
this issue, we establish a new knowledge base embedding framework, called
TIME2BOX, that can deal with atemporal and temporal statements of different
types simultaneously. Our main insight is that answers to a temporal query
always belong to a subset of answers to a time-agnostic counterpart. Put
differently, time is a filter that helps pick out answers to be correct during
certain periods. We introduce boxes to represent a set of answer entities to a
time-agnostic query. The filtering functionality of time is modeled by
intersections over these boxes. In addition, we generalize current evaluation
protocols on time interval prediction. We describe experiments on two datasets
and show that the proposed method outperforms state-of-the-art (SOTA) methods
on both link prediction and time prediction.
