Morphosyntactic disambiguation and segmentation for historical polish with graph-based conditional random fields

Abstract

The paper presents a system for joint morphosyntactic disambiguation and segmentation of Polish based on conditional random fields (CRFs). The system is coupled with Morfeusz, a morphosyntactic analyzer for Polish, which represents both morphosyntactic and segmentation ambiguities in the form of a directed acyclic graph (DAG). We rely on constrained linear-chain CRFs generalized to work directly on DAGs, which allows us to perform segmentation as a by-product of morphosyntactic disambiguation. This is in contrast with other existing taggers for Polish, which either neglect the problem of segmentation or rely on heuristics to perform it in a pre-processing stage. We evaluate our system on historical corpora of Polish, where segmentation ambiguities are more prominent than in contemporary Polish, and show that our system significantly outperforms several baseline segmentation methods.