  We present experiments with part-of-speech tagging for Bulgarian, a Slavic
language with rich inflectional and derivational morphology. Unlike most
previous work, which has used a small number of grammatical categories, we work
with 680 morpho-syntactic tags. We combine a large morphological lexicon with
prior linguistic knowledge and guided learning from a POS-annotated corpus,
achieving accuracy of 97.98%, which is a significant improvement over the
state-of-the-art for Bulgarian.
