Towards a methodology for filtering out gaps and mismatches across wordnets: the case of pl W ord N et and P rinceton W ord N et (2016)

Abstract: This paper presents the results of large-scale noun synset mapping between plWordNet, the wordnet of Polish, and Princeton WordNet, the wordnet of English, which have shown high predominance of inter-lingual hyponymy relation over inter-synonymy relation. Two main sources of such effect are identified in the paper: differences in the methodologies of construction of plWN and PWN and cross-linguistic differences in lexicalization of concepts and grammatical categories between English and Polish. Next, we propose a typology of specific gaps and mismatches across wordnets and a rule-based system of filters developed specifically to scan all I(inter-lingual)-hyponymy links between plWN and PWN. The proposed system, it should be stressed, also enables one to pinpoint the frequencies of the identified gaps and mismatches.

## introduction since the development of the first wordnet, that is, princeton wordnet (henceforth pwn, cf. @xcite , a number of wordnets for the multitude of languages have followed. their construction was usually based on either of the two major approaches: the merge approach assuming manual wordnet creation on the basis of language data collected from dictionaries (e.g. hindi wordnet cf. narayan et al 2001) and the expansion approach taking the content and structure of one of the existing wordnets as input for translation to another language (e.g. indowordnet, @xcite . some wordnets were also built by means of the 'mixed', transfer-andmerge (also called merge-expand) method joining the previously mentioned approaches @xcite @xcite . thus, the process of their construction was often intertwined with the process of their linking to pwn, which served as the 'input' wordnet. the obvious advantage of the expansion and, partly, transferand-merge method is time and cost effectiveness, yet it looses on capturing the actual structure and content of the lexical system of a language in question. one of the few wordnets created independently of pwn is plwordnet, a wordnet of polish language (henceforth plwn), built manually with the help of a unique method of extracting information on lexico-semantic relations from large text corpora (cf. @xcite . although much more timeconsuming and expensive, such method of construction yields a resource which more closely reflects a lexical system of a language. the noun part of plwn has been already linked to pwn using a set of 7 inter-lingual relations (modelled on by those used in eurowordnet, cf. @xcite . all of them were introduced manually by a team of bilingual lexicographers working in accordance with a detailed, three-stage mapping procedure (cf. @xcite . already the first effects of this mapping process have showed a variety of contrasts in the structure and content of plwn and pwn. some of them could be traced to different concept and (partly) grammatical categories' lexicalization between english and polish; other resulted from different con-struction methods of plwn and pwn. the structure of princeton wordnet was motivated by the results of psycholinguistic studies, while its content was largely based on individual lexicographers' choices and the data obtained from monolingual dictionaries. in the paper, we present the results of a final stage of plwn to pwn noun synsets mapping and a proposal of a rule-based system of filters that enables one to identify the sources and measure the degree of gaps and mismatches between the two wordnets. the paper is organised as follows: in section 2 the manual mapping strategy is described and the statistics of inter-lingual relations are given, in section 3 different types of gaps and mismatches revealed in the course of mapping are discussed, in section 4 a procedure for filtering out gaps and mismatches across wordnets is presented, in section 5 the results of filtering are presented, while in section 6 the conclusions are given. ## mapping results mapping between plwn and pwn was carried out by a team of trained and supervised bilingual lexicographers working in accordance with a detailed mapping procedure (cf. @xcite . the mapping was performed on the level of synsets (as in the case of all world wordnets) and consisted in linking plwn and pwn synsets corresponding in meaning and position in wordnet structure by means of one of 7 hierarchically ordered inter-lingual relations, such as synonymy, partial synonymy, inter-register synonymy, hyponymy, hypernymy, holonymy and meronymy. the mapping procedure consisted of three major steps: recognising the sense of the source synset, searching for the most corresponding target synset and selecting an inter-lingual relation to be established. in their work, lexicographers consulted the whole variety of available dictionaries and encyclopedias. also, they were supported by a custom-designed system of automatic prompts, based on the relaxation labeling algorithm paired with a filtering by a large cascade dictionary (cf. @xcite . so far, the process of mapping has been conducted for noun and adjective synsets. the noun part is almost finished, the work on adjective part is still in progress. therefore, in this paper we focus on the results of noun mapping. in one may plausibly argue that the most striking feature of the obtained results is the frequency of i(inter-lingual)-hyponymy links, which is two times higher than the frequency of the 'highest priority' i(nter-lingual)-synonymy links. such results definitely point to a number of discrepancies between the content and structure of the two wordnets. some sources of those discrepancies were already identified @xcite : they encompass those due to the differences between lexical systems of english and polish and those relating to different construction methods of the two wordnets under scrutiny. still, the paper presents and discusses the results of only the very first stage of the mapping process. as shown in in this section, we will discuss, first, the contrasts resulting from different construction methods of plwn and pwn and, second, various types of gaps and mismatches that may occur between lexical systems of natural languages (on the example of english and polish). hence, the main research problem addressed in this paper refers to identification of any gaps and mismatches between linguistic data stored in two electronic lexical databases, that is, pwn and plwn. in general terms, the language-pair specific gaps and mismatches, which will be described in greater detail later in this paper, result from the following factors: 1) differences in structures of pwn and plwn; 2) differences in methodologies used to compile pwn and plwn; 3) specificity of mapping procedure applied to plwn and pwn; 4) systemic differences between english and polish lexicon, morphology and syntax (e.g. varying degrees of lexicalization; differences in encoding of grammatical categories (e.g. gender); varying degrees of morphological productivity of affixal derivation); 5) cross-cultural differences between english and polish. these differences, as applicable to the lexical data stored in plwn and pwn, are discussed in greater detail in the following sections 3.1 and 3.2. ## results that may seem a 'drastic' move, yet we aimed at removing all potential cultural gaps. thus, the number of synsets removed by [filter 3] -3921 -should be treated with caution as it is overestimated, since it also includes synsets that lexicalize concepts common to both polish and english. 3 the abbreviations used to mark relevant registers are explained in with respect to the data presented in ## discussion and conclusions this study constituted an attempt at identifying any gaps and mismatches between lexical data, specifically, nouns, stored in two inter-liked electronic databases, that is, plwn, the wordnet of polish, and pwn, the princeton wordnet of english. the results confirmed our initial hypotheses that the gaps and mismatches result from wordnet-specific structural and methodological differences, specificity of the interlingual mapping procedure, systemic differences between polish and english as well as cross-cultural differences. in order to identify any gaps and mismatches across two aforementioned wordnets, a customdesigned filtering procedure was developed and described in this paper. the results of filtering procedure revealed groups of synsets (mainly gerunds and multi-word synsets) whose existence and high numbers are the effect of the assumed methodology of construction of plwn. next, the procedure revealed groups of synsets such as diminutives, augmentatives and feminine forms that reflect the specificity of the morphology of the polish language and, finally, pwn synsets holding the relation topic-domain and plwn synsets marked for different registers that attest to the presence of culture-dependent concepts were filtered out/identified. the approach presented in this study has a number of limitations which need to be addressed in future research. first, the results revealed up to 28000 synsets that are required to be manually analyzed, the process that is bound to be time-consuming and labour-intensive. second, the procedure described in this paper does not allow, in its current form, checking the filtering results against larger lexical resources (e.g. larger than the cascade dictionary used in this study) where more potential equivalents for polish lemmas could be found. to this end, it is possible to use additional resources such as polish-english parallel corpora (e.g. paralela foot_2 , a large collection of polish-english parallel texts); this could provide an improvement in terms of filtering out the results. a small-scale manually conducted experiment aimed at identification of equivalents in corpora and internet resources has revealed that the number of lemmas present in plwn and, at the same time, not found in the cascade dictionary used in the filtering procedure can be lowered by approximately 37% (see @xcite . finally, it should be stressed that at the current stage there are no means of filtering out exactly those polish synsets whose potential equivalents could be multi-word units with compositional meaning in english. removal of all plwn multi-word synsets with no special tag (cf. @xcite for separate treatment of multi-word units in plwn) as a part of [filter 2] appears to be a significantly imprecise tool with respect to compositionality of meaning, i.e. this operation removed all multi-word synsets in one fell swoop, regardless of the internal semantic dependencies of the words in a multi-word unit. to resolve this problem, it is possible to target the relevant plwn multi-word synsets by identifying instances in which the synsets at hand have hyponymy and meronymy: element relation links to synsets whose lus have the same bases as the lus in question. as for the future, the procedure described in this study and its results may come in useful for exploration of the different types of equivalence relations obtained between lexical data stored in plwn and pwn. this could enable one to turn the study results into actionable knowledge useful for lexicographers and translators, among others.