An Alternate View on Strong Lexicalization in TAG

摘要

TAGs were recently shown not to be closed under strong lexicalization but to be strongly lexicalizable by context-free tree grammars of rank 2. This paper presents an alternative lexicalization procedure that builds on an earlier generalization of TAGs to multi-dimensional trees. A previous theorem that every Tree Substitution grammar is strongly lexical-ized by a corresponding TAG is lifted to higher dimensions to show that for every d-dimensional TAG there exists a (d + 1)-dimensional TAG that strongly lexi-calizes it. A similar lifting reveals that d-dimensional TAGs are not closed under strong lexicalization, so for arbitrary TAGs an increase in dimensionality is an unavoidable consequence of strong lexicalization.