Open D utch W ord N et (2016)

Abstract: We describe Open Dutch WordNet, which has been derived from the Cornetto database, the Princeton WordNet and open source resources. We exploited existing equivalence relations between Cornetto synsets and WordNet synsets in order to move the open source content from Cornetto into WordNet synsets. Currently, Open Dutch Wordnet contains 117,914 synsets, of which 51,588 synsets contain at least one Dutch synonym, which leaves 66,326 synsets still to obtain a Dutch synonym. The average polysemy is 1.5. The resource is currently delivered in XML under the CC BY-SA 4.0 license1 and it has been linked to the Global Wordnet Grid. In order to use the resource, we refer to: https: //github.com/MartenPostma/OpenDutchWordnet.

## introduction the main goal of this project is to convert the dutch lexical semantic database cornetto version 2.0 @xcite into an open source version. cornetto is currently not distributed as open source, because a large portion of the database originates from the commercial publisher van dale. 2 the main task of this project is hence to replace the proprietary content of the database with open source content. in order to create open dutch wordnet, we used all the synsets and relations from wordnet 3.0 @xcite as our basis. we then exploited existing equivalence relations between cornetto synsets and wordnet synsets in order to replace wordnet synonyms by dutch synonyms. we further added new concepts that were not matched through hyperonym relations to the wordnet hierarchy. any new and manually-created semantic relation from cornetto was added to the database as well. we limited the synonyms, concepts and relations to those on which there are no copy-right claims. in addition, the inter-language links in various external resources were used to add synonyms to the resource. the result is an open source wordnet that combines the merge and expand method described in @xcite . the resource is currently delivered in xml under the cc by-sa 4.0 license. 3 in order to inspect and improve the resource, a python module has been created. this module can be found at : https://github.com/martenpostma/ opendutchwordnet . the outline of this paper is as follows. we start with the motivation to create open dutch wordnet in section 2, followed by the methodology to create the resource in section 3. an overview of the main components will be provided in section 4. finally, we discuss the process of making the resource and plans to improve the resource in section 5. ## background and motivation the first version of the dutch wordnet was developed within the eurowordnet project starting from a database developed by van dale publisher. this database already contained synset-like structures and lexical semantic relations that could be used to efficiently derive a wordnet structure. licenses were agreed for commercial and research usage. the dutch wordnet and the referentie bestand nederlands (rbn) @xcite were combined in the cornetto project @xcite . rbn has detailed information on morpho-syntactic, semantic and pragmatic properties of lexical units, with a focus on the combinatorics. the cornetto database thus provides the semantic organization of a wordnet and the details on each synonym in a synset as can be found in lexical unit based lexicons. an important characteristic of cornetto is that it has been developed independently from princeton wordnet (pwn). the synsets in cornetto were then mapped to synsets in pwn following a merge approach @xcite . first, all possible equivalence relations were created between synonyms in synsets using bilingual dictionaries, after which the mappings were ranked on the basis of shared properties, e.g. hyperonyms and hyponyms already linked manually, similar domain labels, and synset membership of multiple translations @xcite . the van dale publisher however decided to stop all collaborations with the research community. this motivated us to develop open dutch wordnet, for which we wanted to keep as much as possible the concepts and word meanings that are defined independently of pwn. this implies that we cannot simply follow an expand approach to translate english synonyms in pwn to dutch words but we need to also match pwn synsets to rbn lexical units. figure 1 introduces the main components of the dutch lexical semantic database cornetto. has hyperonym eq synonym palmboom:1, palm:1 boom:1 palm:3, palm tree:1 <@xmath0, syntax and semantics, especially if these lu's originate from rbn. synonyms that originate from the van dale database only have part-of-speech information. cornetto synsets can have internal semantic relations (isrs) to other cornetto synsets (e.g. has hyperonym), but also equivalence semantic relations (esrs) to pwn synsets (e.g. eq synonym). esrs are mainly used to define synonymy or near synonymy between cornetto synsets and pwn synsets. most isr relations originate from the van dale database. a small set of relations were added manually in the various projects. all synonyms and relations have provenance tags which enables us to trace data from van dale and data that can transferred to the open dutch wordnet. ## methodology we used the following procedure to create open dutch wordnet. we use english wordnet3.0 (pwn) @xcite as our basis for the concept structure. this means that we copied the pwn synsets and relations to odwn and ignored all synsets and relations from van dale. the next step is to transfer the lu's from rbn to the pwnbased synsets. before copying these lu's we improved the quality of the esrs. we defined a set of esrs that are either likely to be more difficult or that play an important role in the transfer. this subset was checked manually and was also used as training to filter the remaining esrs using a decision tree algorithm. this process is described in subsection 3.1. subsequently, we make use of the esrs between cornetto synsets and wordnet synsets to copy the lu's that do not originate from van dale from a cornetto synset into a wordnet synset, which is described in subsection 3.2. the transfer still leaves us with many synsets from pwn without a dutch lu. we therefore use open source resources to translate the wordnet synonyms into dutch, which is described in subsections 3.3 and 3.4, respectively. this results on the one hand in more synsets to have dutch synonyms but also in further evidence for transferred synonyms to be correct because of evidence through other sources. finally, we manually checked 8,257 dutch synonyms, which is described in subsection 3.5. ## overview and statistics in this section, we provide an overview of open dutch wordnet in terms of general statistics, the format it is delivered in, evaluation, and a python module which allows to interact with the resource. open dutch wordnet contains 117,914 synsets, of which the majority are noun synsets: 98,049. there are 18,782 verb synsets and 1,083 adjectival synsets. 51,588 synsets contain at least one dutch synonym, which leaves 66,326 synsets still to obtain a synonym. the resource contains 92,295 synonyms, of which 75,173 are nouns, 15,979 are verbs, and 1,143 are adjectives. the average polysemy is 1.5. 19,996 relations were added to the wordnet hierarchy. ## discussion and future work in this section, we discuss the process of creating open dutch wordnet as well as future work to further improve the resource. a part of open dutch wordnet consists of synonyms that originate from the inter-language links in external resources such as omegawiki, wiktionary, and wikipedia. it is interesting to observe that we obtained mostly noun synonyms from these resources. there are two main reasons why this is the case. firstly, nouns simply have more entries in these resources. in addition, it is obviously more difficult to disambiguate verbs than nouns. in order to get a better understanding of where we added dutch noun synonyms, we visualized the noun hyperonym hierarchy, which can be found in figure 6 . in figure 6 , the noun hyperonym hierarchy is visualized, focusing on which synsets contain a dutch synonym. the lower left side shows a large blue spot, which means that no dutch synonyms are located in that part of the hierarchy. we identified the synset genus ('taxonomic group containing one or more species)' as the main hyperonym of this part. in addition, we observe pink nodes around the top node, which we identified as religious terms such as heer (lord), and jaweh (jaweh). in order to improve the resource, we strive to both improve the quality and quantity of the resource. the quality will be improved by manually inspecting the synsets ranging from 5 to 10 synonyms. the quantity will be improved by adding synonyms in the deeper parts of the resource. this can be done by using more or improved public bilingual resources, both english-dutch but also by combining more languages, or by using parallel corpora. in addition, we plan to assess the most important parts of the hierarchy. this involves the top nodes of the hierarchies and the base concepts. errors in these synsets are likely to propagate to other synsets in lower parts of the hierarchy. finally, the relations imported from cornetto are now added to the pwn relations. as a result, we obtained 115,077 hyperonym relations from pwn and 19,996 hyperonym relations from cornetto. additional hyperonym relations result in tangled hierarchies with more complex semantics. whereas pwn has 559 top nodes for verbs, odwn has 154 tops. the reduction of the tops is due to the additional relations that were created in cornetto to provide more structure to the verb hierarchy. in cornetto, there are only two top nodes for the verb hierarchy. open dutch wordnet currently contains a limited amount of monosemous adjectives. we hope to be able to map the polysemous adjective synsets to pwn synsets by translating the dutch glosses and by making use of the synset relations in cornetto and princeton wordnet. because dutch is very close to german, another possibility is to map the cornetto synsets to germanet @xcite and make use of the rich set of synset relations that it provides. finally, the current format of the resource is xml. we would also like to make the resource available in rdf @xcite . ## conclusion we described open dutch wordnet, which is derived from the cornetto database, princeton word-net and various external resources. we exploited existing equivalence relations between cornetto synsets and wordnet synsets in order to replace wordnet synonyms by dutch synonyms. in addition, the inter-language links in various external resources such as wiktionary and omegawiki were used to add synonyms to the resource. in addition, we manually evaluated each resource and manually edited the most problematic synsets. the princeton-based hierarchy was also extended with manually created relations came from cornetto. open dutch wordnet contains 92,295 synonyms, which are located in 51,588 synsets. there are 75,173 nouns, 15,979 verbs, and 1,143 adjectives. in total, the resource consists of 117,914 synsets, which leave 66,326 synsets still to obtain a synonym. the average polysemy is 1.5. the resource is currently delivered in xml under the cc by-sa 4.0 license. 5 in order to use and improve the resource, a python module has been created. this module can be found at: https://github.com/ martenpostma/opendutchwordnet .