  Semantic role labeling (SRL) -- identifying the semantic relationships
between a predicate and other constituents in the same sentence -- is a
well-studied task in natural language understanding (NLU). However, many of
these relationships are evident only at the level of the document, as a role
for a predicate in one sentence may often be filled by an argument in a
different one. This more general task, known as implicit semantic role labeling
or argument linking, has received increased attention in recent years, as
researchers have recognized its centrality to information extraction and NLU.
This paper surveys the literature on argument linking and identifies several
notable shortcomings of existing approaches that indicate the paths along which
future research effort could most profitably be spent.
