Table 2 Comparison of used tagging schema with the IOB format, where O represents tokens outside of a sequence and I-Frequency represents tokens which are part of a slot filler sequence of type frequency. In contrast, None represents tokens which are neither start nor end token of a slot filler, start:Frequency marks the start and end:Frequency the end of a frequency slot filler sequence

From: Comparing generative and extractive approaches to information extraction from abstracts describing randomized clinical trials