Somewhere between Valency Frames and Synsets. Comparing Latin Vallex and Latin WordNet
Authors: Marco Carlo Passarotti, Berta González Saavedra, Christophe Onambélé Manga (Università Cattolica del Sacro Cuore, 2015)
Topic: Lexical and Semantic Resources and Analysis

Abstract
Following a comparison of the different views on lexical meaning conveyed by the Latin WordNet and by a treebank-based valency lexicon for Latin, the paper evaluates the degree of overlapping between a number of homogeneous lexical subsets extracted from the two resources.

Introduction
Several lexical resources are today available for many languages, ranging from dictionaries to wordnets, ontologies, valency lexica and others. Although such resources deal with the same basic constituents, i.e. lexical entries, these are organized according to different criteria, corresponding to different views on lexicon and, in particular, on lexical meaning. On the one hand, a widespread approach to lexical meaning comes from the basic assumption of frame semantics (Fillmore, 1982), according to which the meaning of some words can be fully understood only by knowing the frame elements that are evoked by those words. Following such an assumption, there is a large use of the concept of valency and of labels for semantic roles in lexical resources. The degree of semantic granularity of the set of semantic roles used is what mostly distinguishes resources like PropBank, VerbNet and FrameNet one from the other. On the other hand, a lexical resource largely used in both theoretical and computational linguistics is WordNet, which is centred on the idea of synonymy in the broad sense. Words are included in synsets, which are sets of words “that are interchangeable in some context without changing the truth value of the proposition in which they are embedded” (from the glossary of WordNet: http://wordnet.princeton.edu). Despite their differences, these two views are not incompatible. Over the last decade, several attempts at linking different lexical resources together have been launched. One of the best known projects is Semlink, which makes use of a set of mappings to link PropBank, VerbNet, FrameNet and WordNet (Palmer, 2009). Pazienza et alii (2006) study the semantics of verb relations by mixing WordNet, VerbNet and PropBank. Shi and Mihalcea (2005) integrate FrameNet, VerbNet and WordNet into one knowledge-base for semantic parsing purposes. Regarding the relations between valency lexica and wordnets, Hlavácková (2007) describes the merging of the Czech WordNet (CWN) with the database of verb valency frames for Czech VerbaLex, whose lexical entries are related to each other according to the CWN synsets. Hajič et alii (2004) use CWN while performing the lexico-semantic annotation of the Prague Dependency Treebank for Czech (PDT), which is in turn exploited to improve the quality and the coverage of CWN. In order to pick out the semantic constraints of the verbal arguments in the Polish WordNet (PolNet), the valency structure of verbs is used as a property of verbal synsets, because it is “one of the formal indices of the meaning (it is so that all members of a given synset share the valency structure)” (Vetulani and Kochanowski, 2014, page 402). Despite a centuries-long tradition in lexicography, the development of state-of-the-art computational lexical resources for Latin is still in its infancy. However, some fundamental resources were built over the last decade. Among them are a WordNet and a treebank-based valency lexicon. In this paper, we present the first steps towards a comparison of these two resources, by evaluating the degree of overlapping of a number of their lexical subsets.

Conclusion
Although a valency lexicon like LV accounts for the different senses that one word may have by assigning it different frame entries, these are not as much semantically defined as the LWN synsets are. However, there is a certain degree of correspondence between these two resources: the more/less fine-grained a frame-based LV subset is, the higher/lower its overlapping with the LWN synsets. For instance, LV includes 1,060 frame entries of verbs formed by an Actor and a Patient: such a subset is both too large and semantically coarse-grained to allow for a sufficient overlapping with the LWN synsets. For this reason, while evaluating the overlapping degree between LV and LWN, we have first focussed on a number of “semantically rich” LV subsets. The evaluation metrics that we used are still very simple. The values of the n-tuples must be weighted at evaluation stage (one sextuple is “heavier” that one triple) and the lexical subsets of LWN must be extended beyond synonymy, by exploiting also other relations between words, like hyperonymy and hyponymy.