  Semitic languages can be highly ambiguous, having several interpretations of
the same surface forms, and morphologically rich, having many morphemes that
realize several morphological features. This is further exacerbated for
dialectal content, which is more prone to noise and lacks a standard
orthography. The morphological features can be lexicalized, like lemmas and
diacritized forms, or non-lexicalized, like gender, number, and part-of-speech
tags, among others. Joint modeling of the lexicalized and non-lexicalized
features can identify more intricate morphological patterns, which provide
better context modeling, and further disambiguate ambiguous lexical choices.
However, the different modeling granularity can make joint modeling more
difficult. Our approach models the different features jointly, whether
lexicalized (on the character-level), where we also model surface form
normalization, or non-lexicalized (on the word-level). We use Arabic as a test
case, and achieve state-of-the-art results for Modern Standard Arabic, with 20%
relative error reduction, and Egyptian Arabic (a dialectal variant of Arabic),
with 11% reduction.
