Highway to Hell. Towards a Universal Dependencies Treebank for Dante Alighieri’s Comedy.
Authors: Claudia Corbetta, Marco Carlo Passarotti, Flavio Massimiliano Cecchini, Giovanni Moretti (Università di Bergamo, Università di Pavia, Università Cattolica del Sacro Cuore, 2023)
Topic: Syntax and Dependency Treebanks

Abstract
In this paper, we describe the creation in Universal Dependencies of a treebank for Dante’s Comedy, the first syntactically annotated text for Old Italian following a dependency-based schema. We detail the phase of treebanking the first part of the Comedy, the Inferno, and we describe some annotation issues. Then, we perform an evaluation of automated dependency parsing with models trained on the currently available annotated portion of the text.

Introduction
Over the past two decades, there has been a growing convergence between the world of corpora for ancient languages and the scholarly community working in the area of technologies for Natural Language Processing (NLP). Because of the absence of native speakers and newly written texts, dealing with ancient languages means lacking the possibility of introspective analysis or field inquiries. The only empirical evidence historical linguists can engage with is confined to old texts, many of which are fortunately digitally available today. Enhancing these data sources with meta-linguistic annotation provides scholars with enriched data to support their investigations. Moreover, building annotated sets of textual data for an ancient language following de facto standards is a way to make these old texts compatible with several ready-made NLP tools, as well as to make them comparable with annotated corpora for other (modern) languages. Universal Dependencies (UD) is an annotation framework started in 2015 which aims to provide a universal formalism for dependency-based syntactic annotation, with the goal of facilitating cross-linguistic comparison. Currently, the project boasts 245 treebanks for 141 languages, including historical languages such as Ancient Greek, Latin, Old French, Akkadian, and Classical Chinese. With regard to the Italian language, there are 9 UD treebanks, covering a diverse range of genres, amounting to 879,657 tokens and 37,871 sentences. This paper details the process of developing a UD treebank out of Dante’s Comedy, starting from the annotation of the Inferno, the first out of the three parts (cantiche) of the work. The motivation for this is the current absence of any dependency-based treebank for Old Italian. Besides providing the scholarly community of historical linguistics with a valuable resource, we create gold data that can be used for the supervised training and testing of stochastic NLP tools. This paper is organized as follows: in Section 2, we introduce Old Italian and the resources available for this language, with a specific focus on the DanteSearch corpus. In Section 3, we describe the creation of the treebank, starting from the Inferno. In Section 4, we describe training and evaluation of a number of models for parsing. Section 5 concludes the paper by summarizing our findings and sketching future work.

Conclusion
Building a UD treebank for Dante’s Comedy is the first step towards incorporating Old Italian among the languages of UD. This paper describes the development of the first part of this treebank, which consists of the first cantica of the Comedy, the Inferno. We also present the results of an experiment of supervised automated dependency parsing using both as training and test sets data from the Inferno. We run this experiment to understand to what extent the process of syntactic annotation of the Comedy, which has been performed so far fully manually, can benefit from the results of the application of an NLP tool. Although the accuracy rates reported in the paper are fairly good (≈77% LAS), in the near future we will have to evaluate how and to what extent they will drop once a model trained and evaluated on the Inferno is applied to a different cantica. Should the accuracy rates drop heavily, even such a negative result might prove helpful in pointing out syntactic differences between the three cantiche. Moreover, the use of other parsers, based on different algorithms and resources (like embeddings), might lead to better and, most importantly, diverging results and errors. As for annotation issues, we will suggest introducing a specific subtype, e.g., ellp, in UD’s documentation, so as to properly identify cases of ellipses, as they are not explicitly captured by the current annotation strategies mentioned in the paper, namely promotion and the use of the relation orphan: the former does not signal the presence of ellipsis, while the latter obscures the real dependency relations which are replaced by it. While adopting a subtype like ellp would make it possible to collect cases of ellipses, their resolution is up to the annotation of so-called enhanced dependencies, which are a kind of advanced annotation that augments dependency labels to facilitate disambiguation. We plan to engage additional annotators with expertise in Old Italian to expedite the process of annotation of Purgatorio and Paradiso. Additionally, we intend to apply error detection processes (like, for instance, those described in [citation needed]) to retrieve possible mistakes or inconsistencies in syntactic annotation. Another task we intend to address is the extension of the UD documentation for Italian in order to make the validator correctly deal with some peculiarities of Old Italian, like for instance enclitic adpositions (e.g., meco ‘with me’), which require the introduction of the feature Clitic=Yes combined with the PoS tag ADP, currently permitted only with the PoS tag PRON. Finally, we plan to include enhanced dependencies in the UD treebank of Dante’s Comedy, once the basic syntactic annotation of the entire work is completed.