An Experiment: Finding Parents for Parentless Synsets by Means of CILI (2023)

Abstract: Identifying and correcting inconsistencies in wordnets is a natural part of their development. Focusing only on the subproblem of missing links, we aim to find automatically possible parents for parentless synsets in IS-A hierarchies of a target wordnet by means of source wordnets where target and source wordnets are in XML-format and equipped with Collaborative Interlingual Index (CILI). In this paper, we describe the algorithm and provide statistics on the possible parents of parentless synsets of the wordnets included in the study. Additionally, we investigate the suitability of the proposed potential parent synsets for correcting noun and verb synsets within the Estonian wordnet.

## introduction one of the main goals of wordnet @xcite development is to make it accessible while ensuring its correctness. the developer must consider that wordnet errors can be formal, semantic, or structural, where formal errors are related to the source file structure or data presentation in it, semantic errors are related to wordnet semantics and structural errors are related to wordnet as a graph @xcite . the category of structural errors is set apart from formal and semantic errors in that it doesn't require any knowledge of the wordnet language, but correcting it requires the assistance of a lexicographer @xcite . 1 an exception is synsets, which are labeled as nouns but are names in terms of content. structural errors often result in missing links between wordnet synsets, which is one of the most obvious problems. this type of problem can appear either as 1) synsets that are completely lacking semantic relationships, as 2) small separate hierarchies, or as 3) a big number of parentless synsets. in identifying parentless synsets for noun and verb synsets, it must be considered that the synsets named as root concepts (or unique beginners) cannot have parents 1 . for example, only one root concept of the is-a noun hierarchy -{entity} -has been considered correct for the princeton wordnet. on the dutch wordnet cornetto (version 2) 2 , however, the corresponding number is two. the same number of root concepts is also assigned to verb hierarchies of cornetto. @xcite . these three examples point to a situation where there is no problem with parentless synsets. nevertheless, this problem is common to all wordnets tested by us in this experiment. for example, the verb hierarchies of open english wordnet (oewn) contain as many as 574 parentless synsets (see the fact that there are synsets with missing links in wordnet has been pointed out by other authors @xcite . however, to the best of the authors' knowledge, no solution has been proposed that automatically provides a possible parent for a parentless synset. this article tries to partially fill this gap, focusing primarily on such missing links, where synset lacks a parent or higher-level concept (superordinate). an additional refinement of the proposed approach comes from the fact that we take advantage of the information available on wordnets equipped with collaborative interlingual index (cili) @xcite . to conduct the experiment, we utilize the following wordnets: estonian wordnet (estwn, version 2.5) foot_0 @xcite , open english wordnet (oewn, version 2021) 4 and six wordnets downloaded from the open multilingual wordnet foot_2 website: open german wordnet (odenet) foot_3 , open dutch wordnet (odwn) @xcite , finnish wordnet (finwn) @xcite , irish language semantic network (lsg) foot_4 , open brazilian wordnet (wn-pt) @xcite , japanese open wordnet (ntu-jpn) @xcite . all eight wordnets are in xml-format and many of their synsets are cili-equipped. the main idea behind our approach is to provide possible parents for parentless synsets in target wordnet using other wordnets. more specifically, this means that a possible parent can only be provided if both the target wordnet synset and its possible parent are equipped with a cili, and so are the synsets from other wordnets corresponding to the same cilis. the paper is organized in the following manner: section 2 formulates the algorithm to find parents for parentless synsets by means of cili. next, section 3 describes the format for reporting the results and provides descriptive statistics about the results obtained. section 4 focuses on the case study of estonian wordnet. section 5 concludes the paper and its findings. ## algorithm each wordnet 𝑤 contains a set of synsets 𝑆. each synset 𝑠 ∈ 𝑆 has a unique id number 𝑖 and might have an optional collaborative inter lingual index (cili) 𝑐 ∈ 𝐶 where 𝐶 is a set of all cilis. id 𝑖 is unique with a wordnet, but each wordnet uses its own set of id numbers. cili 𝑐 is also unique within a wordnet but all wordnets use the same 𝑐 for equivalent synsets. additionally, most (but not all) synsets have hierarchical parent-child relationship structure. however, such relationship might exist in a language but be missing in the wordnet. cilis make it possible to use one wordnet 𝑤 𝑠𝑟𝑐 as a source to estimate the hierarchical parentchild relationship of the other wordnet 𝑤 𝑡𝑔𝑡 (target). the algorithm in this section does this by using a set of cilis 𝐶 𝑠𝑟𝑐 of 𝑤 𝑠𝑟𝑐 , a set of cilis 𝐶 𝑡𝑔𝑡 of 𝑤 𝑡𝑔𝑡 , parent-child relationship map 𝑀 𝑠𝑟𝑐 msrc of 𝑤 𝑠𝑟𝑐 for computing a parent-child relationship map 𝑀 𝑡𝑔𝑡 for 𝑤 𝑡𝑔𝑡 . each cili 𝑐 in 𝐶 𝑠𝑟𝑐 has an associated set of parent cilis 𝑃 𝑐 . each cili 𝑐 ∈ 𝐶 also has an associated id number 𝑖 . therefore, it is possible to construct a map 𝑀 𝑡𝑔𝑡 that represents estimated parent-child relationships for target wordnet 𝑤 𝑡𝑔𝑡 based on similar relations in 𝑤 𝑠𝑟𝑐 . we introduce algorithm 1 to construct such map. we assume that it is trivial to map cili 𝑐 to a corresponding id 𝑖 and will represent this operation as a function 𝑔𝑒𝑡𝑆𝑦𝑛𝑠𝑒𝑡𝐼𝑑𝐵𝑦𝐶𝑖𝑙𝑖(𝑐𝑖𝑙𝑖 ∶ 𝑐, 𝑠𝑒𝑡 ∶ 𝐶). finding parents using a map data structure is also a standard procedure in every programming language, hence we represent this as a function 𝑔𝑒𝑡𝑃𝑎𝑟𝑒𝑛𝑡𝐶𝑖𝑙𝑖𝑠(𝑐𝑖𝑙𝑖 ∶ 𝑐, 𝑚𝑎𝑝 ∶ 𝑀) . the resulting map 𝑀 𝑡𝑔𝑡 contains all found parentchild relations for 𝑤 𝑡𝑔𝑡 based on similar relations in 𝑤 𝑠𝑟𝑐 . therefore, it does not limit the depth of hierarchy, i.e., the algorithm is able to find and store complex and deep hierarchical relations. ## results within this section, we describe the format for reporting the results and provide descriptive statistics about the results obtained. ## conclusion the present study proposed an approach for identifying potential parents for parentless synsets equipped with the collaborative interlingual index (cili) feature using source wordnets. the method is applicable to all wordnets with different languages that have specific xml formats and cili-equipped synsets and has the potential to enhance the quality of wordnets. the experiment revealed that seven out of the eight wordnets analyzed contained a significant number of parentless synsets. however, the majority of these synsets, six out of eight wordnets, had 98% or more parentless synsets that were also equipped with a designated cili. possible parents and grandparents were automatically found for 43% to 99% of the parentless synsets across different wordnets, with 87% or more of the synsets having possible parents in half of the cases. the study indicates that lexicographer involvement may be necessary to correct the identified inconsistencies (missing parents), and that synsets connected through cili in different languages may have different meanings. the proposed approach could also be applied to detect inconsistencies in synsets that already have parents in the future. overall, the method presented in this study provides a useful tool for improving the quality of wordnets across various languages.