Losing a Head in Grammar Extraction

Masaya Taniguchi, Satoshi Tojo

Abstract: The treebank corpus is a collection of the tree that represents a sentence constituency and dependency relation. We are motivated to extract grammar rules from the treebank, that is to decompose the tree data structure and to find grammar rules. After the extraction, we need to validate the adequacy of the grammar so that we inspect the generative power of the obtained grammar. In this phase, the syntactic head is a significant feature, however, in the obtained grammar the head information is missing. Hence, we propose to supplement the lost head information with the type-raising rule of categorial grammar (CG). We extend the same issue to combinatory categorial grammar (CCG) and solve it using the generalized type-raising. Furthermore, we verify our grammar by the formal proof written in the proof assistant system, Isabelle/ HOL.