Tree-Local Multicomponent Tree-Adjoining Grammars with Shared Nodes

Laura Kallmeyer
2005 Computational Linguistics  
This article addresses the problem that the expressive power of tree-adjoining grammars (TAGs) is too limited to deal with certain syntactic phenomena, in particular, with scrambling in freeword-order languages. The TAG variants proposed so far in order to account for scrambling are not entirely satisfying. Therefore, the article introduces an alternative extension of TAG that is based on the notion of node sharing, so-called (restricted) tree-local multicomponent TAG with shared nodes
more » ... ared nodes (RSN-MCTAG). The analysis of some German scrambling data is sketched in order to show that this TAG extension can deal with scrambling. Then it is shown that for RSN-MCTAGs of a specific type, equivalent simple range concatenation grammars can be constructed. As a consequence, these RSN-MCTAGs are mildly context-sensitive and in particular polynomially parsable. These specific RSN-MCTAGs probably can deal not with all scrambling phenomena, but with an arbitrarily large subset. . 1 Additionally, TAG allows for each internal node to specify the set of auxiliary trees that can be adjoined using so-called adjunction constraints and, furthermore, to specify whether adjunction at that node is obligatory. This is an important feature of TAG, since it influences the generative capacity of the formalism: {a n b n c n d n | n ≥ 0}, for example, is a language that can be generated by a TAG with adjunction constraints but not by a TAG without adjunction constraints (Joshi 1985) . For this article, however, adjunction constraints do not play any important role.
doi:10.1162/0891201054223968 fatcat:4lyqkt3wubhxxilnzyqbp4wtaq