Kaplan, Ronald M. & Wedekind, Jürgen: Tractability and Discontinuity
LFG rule systems that embody the explanatory principles of X-bar theory appear to allow for arbitrary repetitions of nodes, particularly complements and coheads, that map to the same f-structure. Such X-bar compliant grammars thus fail to meet the requirements for tractable computation that have been identified in recent work (Wedekind and Kaplan, in press). This raises the question whether those grammars also fail of descriptive accuracy in that they provide for derivations with syntactic dependencies that are not attested in natural languages. We address what may be regarded as a discrepancy between explanatory and descriptive adequacy by imposing finite bounds on the degree of discontinuity of grammatical functions and the number of nodes in functional domains, and by introducing additional filtering conditions on derivations, along the lines of Completeness and Coherence and the original non-branching dominance prohibition, that make it possible to decide that derivations respect those bounds. Grammars that embody the principles of X-bar theory and satisfy these bounds and additional requirements are amenable to tractable processing.
December 22, 2022 |
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