Unsupervised Morpheme Discovery with Allomorfessor

We describe Allomorfessor, which extends the unsupervised morpheme segmentation method Morfessor to account for the linguistic phenomenon of allomorphy, where one morpheme has several different surface forms. The method discovers common base forms for allomorphs from an unannotated corpus by finding small modifications, called mutations, for them. Using Maximum a Posteriori estimation, the model is able to decide the amount and types of the mutations needed for the particular language. The method is evaluated in Morpho Challenge 2009.