We introduce dependency parsing schemata, a formal framework based on Sikkel's parsing schemata for constituency parsers, which can be used to describe, analyze, and compare dependency parsing algorithms. We use this framework to describe several well-known projective and non-projective dependency parsers, build correctness proofs, and establish formal relationships between them. We then use the framework to define new polynomial-time parsing algorithms for various mildly non-projective dependency formalisms, including well-nested structures with their gap degree bounded by a constant k in time O(n5+2k), and a new class that includes all gap degree k structures present in several natural language treebanks (which we call mildly ill-nested structures for gap degree k) in time O(n4+3k). Finally, we illustrate how the parsing schema framework can be applied to Link Grammar, a dependency-related formalism.
Facultade de Informática, Universidade da Coruñna Campus de Elviña, s/n, 15071 A Coruña, Spain. E-mail: firstname.lastname@example.org.
School of Informatics, University of Sussex, Falmer, Brighton BN1 9QJ, UK. E-mail: J.A.Carroll@sussex.ac.uk.
School of Informatics, University of Sussex, Falmer, Brighton BN1 9QJ, UK. E-mail: D.J.Weir@sussex.ac.uk.