What is known about the phonological constraints limiting the form of a Semitic (or even Afroasiatic) root? In other words, are there any limits to the possible sequences of radicals?
For example, per Daya, E., Roth, D., & Wintner, S. (2008). Identifying Semitic roots: Machine learning with linguistic constraints. Computational Linguistics, 34(3), 429-448, the coincidence of the first and second consonants is extremely rare compared to the similarity of 2nd and 3rd. Are there more patterns which allow to predict whether the given C-C-C form (or not threeconsonantal) can be a root, such as some hierarchy of sonority followed, or some sequences banned to avoid their possible contacts when there is no vowel in-between?