Converting an Indonesian Constituency Treebank to the Penn Treebank Format

A constituency treebank is a key component for deep syntactic parsing of natural language sentences. For Indonesian, this task is unfortunately hindered by the fact that the only one constituency treebank publicly available is rather small with just over 1000 sentences, and not only that, it employs a format incompatible with readily available constituency treebank processing tools. In this work, we present a conversion of the existing Indonesian constituency treebank to the widely accepted Penn Treebank format. Specifically, the conversion adjusts the bracketing format for compound words as well as the POS tagset according to the Penn Treebank format. In addition, we revised the word segmentation and POS tagging of a number of tokens. Finally, we performed an evaluation on the treebank quality by employing the Shift-Reduce parser from Stanford CoreNLP to create a parser model. A 10-fold cross-validated experiment on the parser model yields an F1-score of 70.90%.