Delayed Tree Locality and the Status of Derivation Structure

While the derived trees yielded by TAG derivations are uncontroversially taken to correspond to phrase structure, the status of TAG derivation structures as more than a record of TAG operations is less certain. An attractive possibility is to interpret the derivation structure as some representation of semantic meaning, such as a dependency analysis. However, the literature has identified cases where doing so is problematic (Rambow et al., 1995, Candito and Kahane, 1998, Frank and van Genabith, 2001, Gardent and Kallmeyer, 2003, Kallmeyer and Romero 2008), including what has been referred to as the Missing Link Problem: predicates which should have a dependency link are unconnected in the derivation structure. This paper shows that delayed tree-local MC-TAG (Chiang and Scheffler, 2008) provides a solution for certain types of missing links. Further, we observe that the regular form 2-level TAG solutions to the Missing Link Problem given in (Dras et al., 2004) can be reinterpreted using delayed tree-local MC-TAG: the object level derivations of the 2-level TAG derivations can be converted into legal 1delayed tree-local MCTAG derivations. Thus, delayed tree-locality maintains the possibility that TAG derivation structures can be more meaning-laden than solely a record of the combination of trees.