On the mild context-sensitivity of k-Tree Wrapping Grammar

Abstract

Tree Wrapping Grammar (TWG) has been proposed in the context of formalizing the syntactic inventory of Role and Reference Grammar (RRG). It is close to Tree Adjoining Grammar (TAG) while capturing predicate-argument dependencies in a more appropriate way and being able to deal with discontinuous constituents in a more general way. This paper is concerned with the formal properties of TWG. More particularly, it considers k-TWG, a constrained form of TWG. We show that for every k-TWG, a simple Context-Free Tree Grammar (CFTG) of rank k can be constructed, which is in turn equivalent to a well-nested Linear Context-Free Rewriting System (LCFRS) of fan-out k + 1. This shows that, when formalizing a grammar theory such as RRG, which is based on thorough and broad empirical research, we obtain a grammar formalism that is mildly context-sensitive.