A Universal Part-of-Speech Tagset
Table 1: Data sets, number of language specific tags in the original treebank, and tagging accuracies for training/testing on the original (O) and the universal (U) tagset. Where applicable, we indicate whether the data set was extracted from the CoNLL 2006 [Buchholz and Marsi2006] or CoNLL 2007 [Nivre et al.2007] versions of the corpora.
['[BOLD] Language', '[BOLD] Source', '[BOLD] # Tags', '[BOLD] O/O', '[BOLD] U/U', '[BOLD] O/U']
One main objective in publicly releasing this resource is to provide treebank and language specific experts a mechanism for refining these categories and the decisions we have made, as well as adding new treebanks and languages. This resource is therefore hosted as an open source project with version control. Overall, the variance on the universal tagset has been reduced by half (5.1 instead of 10.4). But of course there are still accuracy differences across the different languages. On the one hand, given a golden segmentation, tagging Japanese is almost deterministic, resulting in a final accuracy of above 99%. On the other hand, tagging Turkish, an agglutinative language with and average sentence length of 11.6 tokens, remains very challenging, resulting in an accuracy of only 90.2%.