Packed Levitated Markers
Packed Levitated Markers, or PL-Marker, is a span representation approach for named entity recognition that considers the dependencies between spans (pairs) by strategically packing the markers in the encoder. A pair of Levitated Markers, emphasizing a span, consists of a start marker and an end marker which share the same position embeddings with span’s start and end tokens respectively. In addition, both levitated markers adopt a restricted attention, that is, they are visible to each other, but not to the text token and other pairs of markers. sBased on the above features, the levitated marker would not affect the attended context of the original text tokens, which allows us to flexibly pack a series of related spans with their levitated markers in the encoding phase and thus model their dependencies.