(Almost) Automatic Conversion of the Venice Italian Treebank into the Merged Italian Dependency Treebank Format
Authors: Linda Alfieri, Fabio Tamburini (Università di Bologna, 2016)
Topic: Syntax and Dependency Treebanks

Abstract
This paper describes the automatic procedure we developed to convert an Italian dependency treebank into a different format. We defined about 4,250 formal rules for rewriting dependencies and token tags as well as an algorithm for treebank rewriting able to avoid rule interference. At the end of this process a large portion of the whole treebank was automatically converted, with very few errors, leaving only a small amount of work to be done manually.

Introduction
The availability of large annotated language resources is a prerequisite for the development of reliable automatic annotation tools using machine learning techniques. Automatic tools able to enrich real texts with sentence syntactic structures are central instruments in Natural Language Processing (NLP) pipelines for a reliable annotation of text corpora. Modern NLP parsers heavily depend on complex training phases performed by examining manually annotated treebanks. Data sparsity, especially for low-resourced languages, seriously affect parsers performances, forcing scholars to annotate more and more data. Since 2012 the state-of-the-art for Italian treebanks were not so satisfactory: three different projects and institutions produced three treebanks using different background theories, different formats and also different syntactic structures. They were the Italian Syntactic Semantic Treebank - ISST AUTHOR, the Turin University Treebank - TUT AUTHOR and the Venice Italian Treebank - VIT AUTHOR. Table Pre2012 outlines the main characteristics of these treebanks at that time. TABLE ISST and TUT were used as gold standards in various evaluation campaigns (CoNLL2007 and EVALITA series), but only in 2012 the research groups developing such treebanks started to integrate them into a unique resource. In 2012 the Merged Italian Dependency Treebank - MIDT - was created and released by fusing the two resources AUTHOR and in the following years this project evolved such resource inserting it into the big Universal Dependency - UD - project AUTHOR, through another intermediate step, the Italian Stanford Dependency Treebank - ISDT AUTHOR. During this process some other annotated texts were added to the treebank leveraging its size to around 315,000 tokens and 12,700 sentences (UD\_Italian, v1.3). This paper describes the latest effort for the Italian treebank merging: the conversion, harmonisation and integration of the written sections of VIT, not previously included into ISST, with the other two resources for reaching a global amount of about 600,000 tokens and 23,000 sentences syntactically annotated. For practical issues we decided to convert VIT into the MIDT format and then use the set of already designed automatic procedures and checking programs to transform it into the final UD format. There are other notable works aimed at treebank conversion in various languages, for example we can cite AUTHOR for Italian.

Conclusion
This paper presents the procedure we developed to convert VIT, one Italian treebank, into a different format. Most of the described conversion procedure rely on an automatic algorithm based on formal rules that is able to automatically convert the 81.4\% of the treebank. This procedure can be, in principle, adaptable to any conversion between different dependency treebank formats. The formal rules has been manually defined by using a well known dependency search procedure, Semgrex from StanfordNLP group, properly extended to handle rewriting rules and the final result was manually evaluated to test the effectiveness of the written rules obtaining a very small error rate. To the best of our knowledge, there is no general purpose tool available to automatise this task for dependency graphs. We can find some powerful converters in literature but they are usually tied to specific pair of tagsets (often tailored to the Penn treebank) AUTHOR, and cannot be easily adapted to general needs, or are devoted to tree manipulation, for example the tool `Tregex' AUTHOR. Even if the described procedure can convert a large part of the treebank automatically with a very small quantity of errors, the conversion certainly needs a careful manual analysis to complete the task and check the new treebank for remaining mistakes. The VIT treebank contains a lot of specific and peculiar dependency subgraph for representing phenomena in a very detailed way. Trying to capture all these different variations into formal rules can result in a very large rule set mostly composed of rule that handle single cases. We stopped the production of new rules when this situation arose. We wish to thank Rodolfo Delmonte and Maria Simi for their precious suggestions and explanations for the analysis of linguistic phenomena and for defining the conversion process.