Part-of-Speech Tagging of Northern Sotho: Disambiguating Polysemous Function Words

A major obstacle to part-of-speech (=POS) tagging of Northern Sotho (Bantu, S 32) are ambiguous function words. Many are highly polysemous and very frequent in texts, and their local context is not always distinctive. With certain taggers, this issue leads to comparatively poor results (between 88 and 92 % accuracy), especially when sizeable tagsets (over 100 tags) are used. We use the RF-tagger (Schmid and Laws, 2008), which is particularly designed for the annotation of fine-grained tagsets (e.g. including agreement information), and we restructure the 141 tags of the tagset proposed by Taljard et al. (2008) in a way to fit the RF tagger. This leads to over 94 % accuracy. Error analysis in addition shows which types of phenomena cause trouble in the POS-tagging of Northern Sotho.