Reusing the D anish W ord N et for a New Central Word Register for D anish - a Project Report (2023)

Abstract: In this paper we report on a new Danish lexical initiative, the Central Word Register for Danish, (COR), which aims at providing an open-source, well curated and large-coverage lexicon for AI purposes. The semantic part of the lexicon (COR-S) relies to a large extent on the lexical-semantic information provided in the Danish wordnet, DanNet. However, we have taken the opportunity to evaluate and curate the wordnet information while compiling the new resource. Some information types have been simplified and more systematically curated. This is the case for the hyponymy relations, the ontological typing, and the sense inventory, i.e. the treatment of polysemy, including systematic polysemy.

## introducing cor and dannet the central word register of danishwith the acronym coris a lexicon project running from 2021 to 2023 as part of a danish governmental language technology and ai initiative. the aim of the project is to coordinate, curate, combine and extend already existing lexical nlp resourcesincluding the danish wordnetin a joint initiative in order to ease the use of nlp resources and thereby help boost nlp and language-centric ai for danish. the cor project is funded by the danish agency for digitisation and led in collaboration by three of the main dictionary and lt institutions in denmark: i) the danish language council (dsn), ii) society for danish language and literature (dsl), and iii) centre for language technology (cst) at the university of copenhagen. one of the main ideas in cor is to assign a unique identifier 1 to all lemmas 2 . the main resource consists of a lexicon of the general language vocabulary with basic morphology and semantics. syntactic and phonological information is foreseen in subsequent phases of the project. the lemma selection as well as the morphological information, the glosses and the usage examples are based on three 'classical' dictionaries, the orthographic dictionary retskrivningsordbogen from dsn, the monolingual dictionary den danske ordbog (the danish dictionary, ddo) and the thesaurus den danske begrebsordbog (the danish thesaurus, ddb) from dsl. the formal semantic information in cor (labelled cor-s), in contrast, relies to a large extent on the danish wordnet, dannet @xcite ), but also includes data from the danish 1 which can be seen as a parallel to the danish person register (cpr) where all danish citizens are assigned a unique id. 2 see also the cor description on the website of the danish language council (in danish): https://dsn.dk/nyheder-ogarrangementer/dansk-sprognaevn-med-i-storsprogteknologisk-satsning/ ## cor-s as related to other danish lexical resources as has been described in previous accounts (pedersen et al. 2022 and others), all nlp resources including dannet are linked at sense level with the sense inventory of the ddo. this means that the semantic nlp resources are all conferring to the same sense and lemma inventory and that an integration of information types is therefore more or less straight-forward. as depicted in figure 1 , cor-s is mainly compiled on the basis of dannet, but as mentioned above, including the integration of further information from primarily ddo, the danish thesaurus (surrounding words), the danish sentiment lexicon (connotation polarity), and the danish frame-net (semantic frames on verbs and deverbal nouns). ## hyponymy revisited the skeleton of the wordnet in the sense of its hyponymy structure is essentially taken over in cor, meaning that all senses in cor include a link to its most suited hypernym. some adjustment has however taken place. for instance, very specialist taxonomies are simplified to a certain extent, reflecting now to a larger degree a layman's perspective to i.e., natural entities (e.g., plants and animals). the hypernyms of abstract and verbal entities in dannet (denoted as 2 nd and 3 rd order entities, respectively, according to lyons' semantic divisions @xcite ) often relate to synsets that are based on highly polysemous ddo lemmas. these were therefore in some cases incorrectly assigned and have now been adjusted. for instance, the inventory of verbal hypernyms has been reduced to ensure consistency among verbs. our goal is to cover all dannet hypernyms in cor-s, and in the final phase to convert the synsets to the corresponding cor-s senses. the task is somewhat complicated by the simultaneous overall reduction of senses in cor, meaning that two dannet synsets might result in only one cor-s sense according to a set of principled reductions rules (see section 5). ## a slightly simplified ontological typing dannet contains ontological typing on all synsets conferring to the eurowordnet ontology @xcite ) with a few extensions, such as an additional type denoting body parts, which seems to a very frequent ontological type with specific characteristics. for cor, however, we generally aim at a much simpler and more intuitive ontology that can easily be managed and understood also by non-experts and where a high degree of consensus can be achieved in a first encoding round. to this end, the ontology has been radically simplified, reducing the number of types by 36% from 204 to 130. for example, approx. 1/8 of the eu-rowordnet ontological values were only applied 10 times or less in dannet signaling thereby their somewhat unconsolidated status. therefore, we decided to remove these in cor-s 3 . since the aspectual distinction between bounded and unbounded events is rarely lexicalized in danish (but rather determined by the surrounding adverbs, adverbial particles, or prepositional phrases), we decided to neglect this meaning component in cor-s, a fact that also reduces the number of types significantly. some of the most complex 2nd order types describing several meaning components at a time in different combinations (purpose, social, as well as possession, for example) were also omitted. instead, the lexicographer must decide on the most prominent meaning aspect when assigning a type. finally, the names of the types were in some cases changed into more intuitive ones (3rd orderentity is changed to abstract, 2ndorderentity+agentive to act and so forth). see where most transfer from the eurowordnet ontology to the cor ontology is done fully automatically (many -> one), a few are left for manual inspection to select the most prominent meaning component among several. this is the case for instance where both the meaning components purpose and social are encoded in the source, and where we in cor select what we consider to be the most prominent, as in drille (to tease): social. ## a reduced sense inventory suitable for nlp another characteristic feature of cor-s compared to most other available lexical resources for danish, is its reduced sense inventory. this feature has been suggested by nlp developers to ease word sense disambiguation and overall make the resource more directly applicable in practical nlp tasks, an approach that corresponds well to positions put forward for instance by @xcite . in @xcite we report on the lexicographical principles behind this sense reduction in cor to what we label core senses, and which can be summarized as follows: ## systematic polysemy in a reduced sense inventory systematic polysemy constitutes a particular case of ambiguity where multiple lemmas show the same, regular pattern of polysemy. the phenomenon is well described in literature @xcite @xcite and has been dealt with in both lexicography and in linguistics more broadly, relating to whether you tend to represent the phenomenon by splitting or merging the sensesor by something in between foot_1 . a general aim in all approaches is to try and treat the phenomenon consistently, which, however, is not as easy as it sounds at least not in a fully-fledged lexicon. for instance, the merge principles defined in section 5 cannot really serve as guidance here since the ddo as source applies mostly extralinguistic principles for describing lemmas that are systematically polysemous, such as space principles in the original printed dictionary in combination with the frequency of the lemma foot_2 . therefore, to get an overview of the phenomenon in danish, and to subsequently outline consistent merge or split principles for cor-s (as well as to encode the pattern value as part of the semantic information for each sense), we have been through a large set of lexicographical material based on the aforementioned core vocabulary and have identified more than 20 patterns of systematic polysemy. for an in-depth account of this work, see @xcite . for each pattern we have decided whether to keep the distinction of the senses or merge them into a single sense. here, we reused the work already done in dannet with respect to clarifying systematic polysemy (see @xcite ) since the patterns become obvious both from the ontological types and from the hypernym structures. for instance, the distinction between living and non-living entities in the dannet taxonomy reveals the animal/food pattern, and these senses are maintained in cor-s since they are quite clearly distinguished in use. in addition, the frequency of a particular sense type plays a role. to this end, in the related pattern animal body part/food the principle says to merge due to the proportionally much higher frequency of the food sense here (we only very rarely talk about e.g. chicken breasts or chicken wings outside the cooking scenario). for the process/result pattern, to give another example, we only split senses when the result is a concrete artifact and thus distinguishes itself clearly from the process (as is the case for konstruktion 'construction'). ## cor as feedback to danne in the cor project, a lemma that is only represented in one of its senses in dannet is considered from a semasiological perspective, meaning that a con-siderable amount of supplementary information is encoded to it. when the cor project ends in 2023, we will therefore consider which of this curated information should be transferred back to dannet with the aim of improving the wordnet. the id numbers ensure that this should not be too difficult a task. first of all, dannet does not contain all senses of a lemma in the way that cor-s does (even if for cor-s, we merge senses). this is a flaw of dannet, which was produced under hard time constraints and which had hypernyms with many hyponyms as a driving principle leaving sometimes quite central senses untreated. secondly, the dannet senses that have being deemed rare or too domain specific via the examinations in cor-s (approx. 10%) should be labeled as such in dannet since the information is relevant for several purposes. some senses in dannet are lumped together in cor-s, and it should be considered whether also to reflect this in dannet in some way. the validation of the hypernyms in cor-s also provides useful feedback to dannet and calls for a similar curation in the original resource. last but not least, it might be fruitful to adopt the more coarse-grained version of the euroword-net ontology developed in cor, and in this case also transfer the validated ontological types from cor back to dannet to ensure a higher lexical quality of the wordnet, especially in the case of 2 nd and 3 rd order entities where the eurowordnet ontology has proven somewhat complex to use in practice. sentiment values will already be directly included in dannet based on the underlying data of the sentiment lexicon @xcite (describing values at sense level). finally, the integration of semantic frames in dannet is still under consideration as a way to improve the verbal descriptions in the resource. ## concluding remarks building a new lexical resource like cor is an expensive and extremely time-consuming task. the cor project is primarily meant to serve the nlprelated ai industry by providing an easy-to-use, open-source resource with unique identifiers. in such a case, it seems indispensable to look around in the language community for resources that can be easily reused for that particular purpose. as well as to consider lexicographical standards that can ease transfer and alignment, as underlined in the lexicographic elexis infrastructure @xcite . as has been shown in this paper, we have had the great advantage in the danish language community of having several substantial semantic resources interlinked via a unified sense id structure and relying on international standards. this has enabled us to easily transfer information into the new resource. in particular, the danish wordnet, dannet (in combination with ddo) has proven useful for this task. while going through dannet for the purpose of compiling cor, we have further taken the opportunity to also consider which revisions we would like to transfer back to the wordnet at a later stage in order to improve this stand-alone resource. in this way, the cor project has given us the chance to actually curate a resource that was compiled more than 10 years ago as part of a research project with only limited resources