Building a Treebank in Universal Dependencies for Italian Sign Language
Authors: Gaia Caligiore, Cristina Bosco, Alessandro Mazzei (Università di Torino, 2020)
Topic: Lexical and Semantic Resources and Analysis

Abstract
The Italian Sign Language (LIS) is the natural language used by the Italian Deaf community. This paper discusses the application of the Universal Dependencies (UD) format to the syntactic annotation of a LIS corpus. This investigation aims in particular at contributing to sign language research by addressing the challenges that the visual-manual modality of LIS creates generally in linguistic annotation and specifically in segmentation and syntactic analysis. We addressed two case studies from the storytelling domain first segmented on the ELAN platform, and second syntactically annotated using CoNLL-U format.

Introduction
The Italian Sign Language (LIS) is the natural language used by the Italian Deaf community. Signed languages have been extensively studied in the last years (Brentari, 2010). From a theoretical point of view, Signed languages are of interest to the linguistic domain since they are multi-channels natural languages, where the coexistence of different articulators (hands, face, lips, posture, feet, etc.) is the test-bed for the formalization of new linguistic theories or objects (e.g. (Huenerfauth, 2006)). From a practical point of view, there is a real necessity to design and realise automatic translators for Deaf communities (Bragg et al., 2019). We want to investigate LIS with the same means used for Vocal Languages (VL) and verify if, in doing so, LIS can be properly represented. In this context, language-specific strategies and resources should be developed. The reference framework in this work is the Universal Dependencies formalism (UD), a de facto standard for syntactic annotation. The main goals of this research are three. The first goal is theoretical. We want to investigate the expressiveness of UD tags and its relations with LIS. Signed languages have peculiar forms of lexicons and syntax and we want to experimentally verify the expressive power of the UD formalism in representing this richness. The second goal is theoretical as well. We want to determine the extent of the similarities and differences in syntactic constructions between Italian (as reported in the Italian-UD (Simi et al., 2014)), Swedish Sign Language (SSL, as reported in the SSL-UD treebank (Mesch and Schonstrom, 2018)) and LIS. At the present moment, the SSL is the only sign language that has been annotated on UD. The SSL treebank is comprised of 203 sentences taken from the Swedish Sign Language Corpus (SSLC) (Mesch and Schönström, 2018; Mesch and Wallin, 2015). Being the only reference for the construction of a treebank for a sign language, the SSL treebank was a fundamental resource for the choice of the direction to follow in the annotation of LIS, particularly with regard to the first step of the process, i.e. the segmentation on ELAN (see section 2.1). The third goal is more practical. We want to create a UD compliant resource for the syntactic annotation of LIS: the first LIS-UD treebank. To our knowledge, apart from the domain-specific bilingual corpus developed in the projects ATLAS and LIS4ALL on automatic translation (Mazzei et al., 2013; Geraci et al., 2014; Mazzei, 2015), this is the first attempt to use dependency relations for representing LIS syntax. For building the corpus, we selected two case studies in the storytelling domain: all of the sentences of two LIS videos, namely the fairy tale Cappuccetto Rosso (Little Red Riding Hood) and the story I tre fratelli (The three brothers, written by the Italian writer Grazia Deledda), were collected in the novel treebank that, at the moment, is comprised of 257 dependency trees. While in the Cappuccetto Rosso story the signer signs the story without an Italian reference text, in the I tre fratelli story the signer is translating from a well defined written Italian text. By using the full original version of these stories, we had to face the challenge represented by unrestricted real data. For instance, very long and complex sentences were annotated and translated into LIS. Considering the intrinsic complexity of the task and the novelty of the project, in the preliminary release of data described in this paper we only addressed some of the features of LIS. For instance, the location in space of a sign is only annotated in the portion of analysis carried out on ELAN but was not transferred in the CoNLL-U files. Furthermore, non-manual elements – which are one of the fundamental means used by LIS signers to convey meaning (Volterra, 2004)– are not included in any annotation layer developed in this project. This is the result of a lack of a more appropriate annotation strategy that is specific to sign languages within the UD framework, which is originally developed for the analysis of VLs and, by default, does not include the possibility to annotate the features of a language that go beyond the alphabetical construction of a word (or gloss, in this case). The paper is organized as follows. In the Section 2, the data collection and the morphological and syntactic annotation processes will be described. In Section 3, language-specific morphosyntactic phenomena are discussed mainly focusing on pointing signs as Highly Iconic Structures (henceforth HIS). The strategies used to annotate signs and their dependency relations are justified. Section 4 concludes the paper by providing some issue on the future development of the project.

Conclusion
The paper describes the development of the novel resource LIS-UD, namely a treebank for LIS in the UD format. Provided the preliminary stage of the project, the main aim of this work is to discuss the issues raised by the annotation in UD of a sign language. This issue has previously been only partially addressed in one other single project for the development of the SSL treebank, and so the novel resource can be the opportunity for better investigating it. Several future directions can be drawn for the development of our project. In particular, among these directions, we are planning first of all to draft a more detailed document about the annotation guidelines. This can help us in checking the material annotated until now, but also in driving the work of novel annotators.