Case in XTAG

The English XTAG grammar adopts the notion of case and the case filter for many of the same reasons argued in the GB literature. However, in some respects the English XTAG grammar's implementation of case more closely resembles the treatment in Chomsky's Minimalism framework [#!chomsky92!#] than the system outlined in the GB literature [#!chomsky86!#]. As in Minimalism, nouns in the XTAG grammar carry case with them, which is eventually `checked'. However in the XTAG grammar, noun cases are checked against the case values assigned by the verb during the unification of the feature structures. Unlike Chomsky's Minimalism, there are no separate AGR nodes; the case checking comes from the verbs directly. Case assignment from the verb is more like the GB approach than the requirement of a SPEC-head relationship in Minimalism. Most nouns in English do not have separate forms for nominative and accusative case, and so they are ambiguous between the two. Pronouns, of course, are morphologically marked for case, and each carries the appropriate case in its feature. Figures 4.3(a) and 4.3(b) show the NP tree anchored by a noun and a pronoun, respectively, along with the feature values associated with each word. Note that books simply gets the default case nom/acc, while she restricts the case to be nom.

  

Figure 4.3: Lexicalized NP trees with case markings

(a)		(b)