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LAF/GrAF-grounded Representation of Dependency Structures

This paper shows that a LAF/GrAF-based annotation schema can be used for the adequate representation of syntactic dependency structures possibly in many languages. We first argue that there are at least two types of textual units that can be annotated with dependency information: words/tokens and chunks/phrases. We especially focus on importance of the latter dependency unit: it is particularly useful for representing Japanese dependency structures, known as Kakari-Uke structure. Based on this consideration, we then discuss a sub-typing of GrAF to represent the corresponding dependency structures. We derive three node types, two edge types, and the associated constraints for properly representing both the token-based and the chunk-based dependency structures. We finally propose a wrapper program that, as a proof of concept, converts output data from different dependency parsers in proprietary XML formats to the GrAF-compliant XML representation. It partially proves the value of an international standard like LAF/GrAF in the Web service context: an existing dependency parser can be, in a sense, standardized, once wrapped by a data format conversion process.