Merging D an N et with P rinceton W ordnet (2019)

Abstract: In this paper we describe the merge of the Danish wordnet, DanNet, with Princeton Wordnet applying a two-step approach. We first link from the English Princeton core to Danish (5,000 base concepts) and then proceed to linking the rest of the Danish vocabulary to English, thus going from Danish to English. Since the Danish wordnet is built bottom-up from Danish lexica and corpora, all taxonomies are monolingually based and thus not necessarily directly compatible with the coverage and structure of the Princeton WordNet. This fact proves to pose some challenges to the linking procedure since a considerable number of the links cannot be realised via the preferred cross-language synonym link which implies a more or less precise correlation between the two concepts. Instead, a subpart of the links are realised through near synonym or hyponymy links to compensate for the fact that no precise translation can be found in the target resource. The tool WordnetLoom is currently used for manual linking but procedures for a more automatic procedure in future is discussed. We conclude that the two resources actually differ from each other quite more than expected, both vocabulary and structure-wise.

## linking complexities due to taxonomical differences a major challenge when merging two wordnets concerns the often found discrepancies in taxonomical structure @xcite . taxonomical discrepancies may have different origins, such as: in our linking work, we encounter discrepancies of all three types. where dannet is compiled on the basis of a layman's dictionary of danish, pwn is compiled without basis in any specific previous resource, but generally more true to expert knowledge in particular in relation to i.e. natural taxonomies. consider the taxonomical complexity of the concept plante ('plant') in dannet in figure 2 compared to that of pwn in figure 3 . even if the graphical interfaces differ, it proves quite evident that dannet uses a layman's much simpler organization principles of plants than does pwn. another overall discrepancy worth mentioning is different approaches taken wrt. the treatment of systematic polysemy. for instance, in dannet all countries have a 'geographical' and a 'people' reading, a dichotomy which is not equally found in pwn and which makes a one-toone linking procedure impossible. figure 3. plant with hyponyms in pwn cultural differences regarding how for instance the educational or the juridical system is organized is also clearly reflected in the taxonomical structures. finally, pure idiosyncracies are found all over the resources, maybe even to some extent also culturally based; for instance cheese has a taxonomical division of concepts in dannet (figure 4 ) based on whether the cheese is cut or spread on the bread (typically on open sandwiches of rye bread); a division which is not made in pwn. 4 core concepts: linking complexities and lexicographic characteristics the core concepts of pwn have been selected based on two criteria: importance of synsets measured by a) the number of relations with other synsets and b) a high position in the hierarchy. oflazer & murat (2018) describes how the six balkanet wordnets successfully used the latter criterion, a relatively high level of the english words in the pwn hierarchy, as a common starting point for the expand method, based on the assumption that language-specific information gets more important as one moves down the hierarchy. also @xcite states that concepts at a basic level are more likely to be shared across classificatory systems than concepts at more general or more specific levels. in our case this is confirmed. as already described in section 2, the linking process of the core concepts when going from pwn to dannet results in many direct links, and equivalents were likely to be part of vocabulary covered by dannet -only in a few cases new synsets had to be created. the fact that dannet is linked directly to a medium-sized corpus-based monolingual dictionary giving access to all types of lexical information now allows us to study the lexicographic characteristics of the core vocabulary in detail. we would in the case of danish expect the core concepts to be simplex words rather than compounds and are now able to find out whether it is in fact the case. simplex lemmas in ddo are opposite to compound lemmas characterized by often being part of the manually selected ~65,000 lemmas that constituted the vocabulary of the first printed version of the dictionary, and thereby to carry information on etymology, phonetics and compounding to a much higher degree than the ~35,000 lemmas added in the later years, after the first published edition. as seen in when it comes to the challenges caused by different sense granularities in the two lexical resources, the danish lexicographers who mapped the core concepts often got the impression that the sense inventory of pwn was more fine-grained than the one of dannet/ddo. this seems to be for a good reason. when studying 20 highly polysemous danish nouns with their english equivalents (see ## linking complexities of non-core concepts (going from dannet to pwn) when it comes to the vocabulary of the non-core concepts, the linking complexities are of a different nature. one might think that the task of mapping less polysemous words would be easier, but confirming the assumptions of oflazer & murat, (2018) mentioned in section 4, it seems that language-specific peculiarities tend to evoke more translation difficulties as one moves down the hierarchy. in spite of their considerable size, the two lexical resources cover quite different vocabulary and it is often difficult to find exact equivalents. although the two wordnets seem to have more or less the same level of specificity, it is not carried out in detail for exactly the same vocabulary. sometimes pwn is more specific wrt. to hyponyms than dannet, and sometimes dannet covers the highest number of specific concept lemmas, typically in the form of compounds. as an example to this, the noun forhandling ('negotiation') has 13 hyponyms in dannet, all compounds, e.g. kontraktforhandling ('contractual negotiations'), skilsmisseforhandling ('divorce proceedings'). the english equivalents are not included in oed, nor in pwn. and the english equivalent to the hypernym forhandling ('negotiation') has no hypernyms in pwn. even when it comes to mapping the hyponyms of concrete core concepts which are already mapped, and where we find roughly the same number of hyponyms in the two wordnets, we might still not find many equivalents among these hyponyms. compare for example the types of carpets in dan-net, the hyponyms of taeppe (axminstertaeppe, bedetaeppe, kludetaeppe, kokostaeppe, løber, perser, rya, måtte, filttaeppe, forligger, sengeforligger, taeppebelaegning) in figure 5 with the types of carpets in pwn, the hyponyms of rug in pwn in figure 6. among the 14 english hyponyms, only prayer carpet, runner, scatter rug and shag rug have danish equivalents among the 12 hyponyms of taeppe. figure 6. hyponyms of rug in pwn also culture-specific differences as discussed in section 3 result in many lexical gaps. this is a problem that wordnet developers encounter even when applying the expand model in the first place. in balkanet for example, once a core wordnet was developed by translating from pwn, the 6 language partners had to add a number of languagespecific synsets which were afterwards linked to pwn via hypernymy relations @xcite . in our case such synsets are already included in dannet and have danish hypernyms, and they are now supplied with an english hypernym as well, also in cases where an english translation equivalent does in fact exist but is not (yet) part of pwn. one example is the vocabulary of handball, a common sport in denmark, however less important in the anglo saxon community and therefore not (yet) included in pwn. finally it should be mentioned that some linking complexities are caused by differences in word formation in danish and english. where nounnoun compounding is indeed very productive in danish, english in many cases construct similar content by using an attributive and a noun. for example, compounds with andels-(co-op, cooperative) e.g. andelssamfund and andelsbutik translate into english by using an attributive and a noun as in 'cooperative society', 'cooperative store'. there seems to be a tendency that such terms are not lexicalized in english to the same degree and thus not present in pwn. ## the linking tool for the linking from dannet to pwn (which is currently ongoing) we apply the wordnet editing system wordnetloom 2.0 @xcite . wordnetloom is a graph-based system where several users can access and edit the nodes (lexical units) edges (semantic relations), and synsets as well as view glosses and usage examples. the complex ontological types of the synsets (following the eurowordnet top-ontology @xcite ) are also visible in the accustomed version suitable for browsing dannet, developed by tomasz naskręt 5 and adapted by mitchell j. seaton foot_2 . an advantage of the system is that users can view and directly edit the relations in the interface, avoiding problems on manual editing of a wordnet representation file. as seen at the top of figure 7 shows an example where avisbud 1 ('paper deliveryman') is placed between 'deliveryman 1' as a hypernym, and 'newsboy 1' as a hyponym. avisdreng 1 is synonymous with 'newsboy 1', which is nearly the same as 'paperboy 1'. every relation can be established, edited or deleted. the synonym, near-synonym, hypernym and hyponym relations (see the green lines) are prioritized 5 g4.19 research group, department of computational intelligence wrocław university of science and technology, wrocław, poland (in that order) when linking. the relation is chosen from a drop-down menu as seen in figure 8. ## concluding remarks the merging of dannet with pwn is still ongoing and proves both cumbersome and complex as we have exemplified in the previous sections. to speed up the process, we hope to be able to introduce more semi-automatic procedures at a later stage when a substantial number of links have already been established, even if it has become evident that manual inspection and correction will always be a considerable part of the job. within the elexis project the naisc tool (mccrae 2018) will soon be available and we hope to examine to which degree a semi-automatic linking with this tool involving interaction between lexicographers and developers can be useful. it has generally been a surprise to us to acknowledge to which extent the two resources actually differ, both vocabulary-and structurewise. a fact which has made us realize that a merge of the resources will really only be approximate. nevertheless, it is our conviction that even such an approximate merge will be useful for several future nlp tasks where danish is involved. further, in line with the goals of the elexis project, we hope that it will help interconnect existing resources in the lexicographical milieus in europe. as such, the merge will provide the interlingual access to a substantial part of the lexical resources available for danish.