Tagging Semantic Types for Verb Argument Positions
Authors: Francesca Della Moretta, Anna Feltracco, Elisabetta Jezek, Bernardo Magnini (Università di Pavia, Fondazione Bruno Kessler, University of Bergamo, 2017)
Topic: Lexical and Semantic Resources and Analysis

Abstract
Verb argument positions can be described by the semantic types that characterise the words filling that position. We investigate a number of linguistic issues underlying the tagging of an Italian corpus with the semantic types provided by the T-PAS (Typed Predicate Argument Structure) resource. We report both quantitative data about the tagging and a qualitative analysis of cases of disagreement between two annotators.

Introduction
Words that fill a certain verb argument position are characterised for their semantic properties. For instance, the fillers of the object position of the verb ``eat" are typically required to share the fact that they are edible objects, like ``meat" and ``bread". There has been a vast literature in lexical semantics addressing, under different perspectives, this issue, including the notion of selectional preferences AUTHOR AUTHOR, the notion of prototypical categories AUTHOR, and the notion of lexical sets AUTHOR AUTHOR. However, despite the large theoretical interest, there is still a limited amount of empirical evidences (e.g. annotated corpora) that can be used to support linguistic theories. Particularly, for the Italian language, there has been no systematic attempt to annotate a corpus with semantic tagging of verb argument positions In this paper we assume a corpus-based perspective, and we focus on manually tagging verb argument positions in a corpus with their corresponding semantic classes, selected from those used in the T-PAS resource AUTHOR. We make use of an explicit set of semantic categories (i.e., an ontology of Semantic Types), hierarchically organised (e.g. inanimate subsumes food): we are interested in a qualitative analysis, a rather different perspective with respect to recent works that exploit distributional properties of words filling argument positions AUTHOR. We run a pilot annotation on a corpus of sentences. We aim at investigating how human annotators assign semantic types to argument fillers, and to what extent they agree or disagree. A mid term goal of this work is the extension of the T-PAS resource with a corpus of annotated sentences aligned with the T-PASs of the verbs (see section 2). This would have a twofold impact: it would allow a corpus based linguistic investigation, and it would provide a unique dataset for training semantic parsers for Italian. The paper is structured as follows. Section 2 introduces T-PAS and the ontology of semantic types used in the resource. Section 3 describes the annotation task and the guidelines for annotators. Section 4 presents the annotated corpus and the data of the inter-annotator agreement. Finally, Section 5 discusses the most interesting phenomena that emerged during the annotation exercise.

Conclusion
We performed a pilot experiment to tag the arguments of verbs, as recorded in the T-PAS resource, with their associated semantic type. We obtained good result in the annotation. By analyzing the cases of inter annotator disagreement, we were able to identify phenomena which lie at the core of such disagreements, such as the presence of inherent polysemous words. Ongoing work includes spelling out the rules for polysemous words tagging more clearly in the guidelines.