Enriching Open Multilingual Wordnets with Morphological Features
Authors: Stefania Racioppa, Thierry Declerck (German Research Center for Artificial Intelligence, Austrian Academy of Sciences, 2019)
Topic: Lexical and Semantic Resources and Analysis

Abstract
In this article, we describe our work on porting Open Multilingual Wordnet resources into the OntoLex-Lemon model, in order to establish an interlinking with corresponding morphological resources, such as the MMorph resource set. For this purpose, the morphological resources were also ported onto OntoLex-Lemon. We show how the “lemmas” contained in the Wordnet resources can be enriched with morphological features using the lexical representation and linking features of OntoLex-Lemon, which support, among others, the formulation of restrictions in the usage of such expressions. Our work will result in an improved lexical resource combining Wordnet senses and full morphological descriptions in a single ontological framework, as specified in the OntoLex-Lemon model.

Introduction
WordNets are well-established lexical resources with a wide range of applications. For more than twenty years they have been elaborately set up and maintained by hand, especially the original Princeton WordNet of English (PWN) (Fellbaum, 1998). In recent years, there have been increasing activities in which open WordNets for different languages have been automatically extracted from various resources and enriched with lexical semantics information, building the so-called Open Multilingual Wordnet (OMW) (Bond and Paik, 2012). These WordNets were linked to PWN via shared synset IDs (Bond and Foster, 2013; Bond et al., 2016). The resources in OMW are of different coverage and contain not always the same amount of information, as for example many resources are lacking definitions (or “glosses”), contrary to the PWN resource, or example sentences. The work described in the present article is an extension of previous experiments done with English (Gromann and Declerck, 2019) and more recently with German lexical semantics resource, as we wanted to consider languages with a complex morphology. In the present article we focus on Romance languages, especially Italian. Our current work deals primarily with the morphological enrichment of OMW resources for Italian, i.e. “ItalWordNet.” The first morphological resource we took into consideration for this purpose is an updated version of the MMorph morphological analyser (Petitpierre and Russell, 1995). As a representation mean we chose OntoLex-Lemon (Cimiano et al., 2016), as this model has proven to be able to represent both a classical lexicographic description (McCrae et al., 2017) as well as lexical semantics networks like WordNet (McCrae et al., 2014). OntoLex-Lemon is a further development of the “Lexicon Model for Ontologies” (lemon) (McCrae et al., 2012). Following the Guidelines for mapping Global WordNet formats onto lemon-based RDF, some WordNets have already been mapped onto the former lemon model (McCrae et al., 2014). Our present goal is thus to integrate conceptual descriptions, lemmas and morphological descriptions in the extended ontological framework specified by the OntoLex-Lemon model. In the next sections, we give some background information on OMW and MMorph. We continue with a section on OntoLex-Lemon, followed by sections that describe how OntoLex-Lemon supports the linking of lemmas in the OMW resources to full morphological descriptions. Doing so, morphological descriptions can be associated with the conceptual entries of WordNet.

Conclusion
We described our work on porting Open Multilingual Wordnet resources into the OntoLex-Lemon model, in order to establish an interlinking with corresponding morphological resources, such as the MMorph resource set. For this purpose, the morphological resources were also ported onto OntoLex-Lemon. As a result we noticed that this model can be easily used for bridging the WordNet type of lexical resources to a full description of lexical entries, which could possibly lead to an extension of the coverage of WordNets beyond the consideration of lemmas and PoS information. We documented our interlinking work with the example of the full morphological representation of Italian words, putting them in relation with the corresponding OMW data sets. We also started to investigate the description of usage restrictions, which allows us to state formally that certain Wordnet concepts should be used only in the singular or in the plural form. As a final goal of our work, we see the interlinked or merged resources in the Linguistic Linked Open Data (LLOD) cloud. We will investigate how our work can be combined with resources present in the LLOD, especially with the BabelNet framework, which is already integrating a huge number of lexical resources, including Princeton WordNet, and encyclopedic data sets (Ehrmann et al., 2014).