Toward a truly multilingual G lobal W ordnet Grid (2016)

Abstract: In this paper, we describe a new and improved Global Wordnet Grid that takes advantage of the Collaborative InterLingual Index (CILI). Currently, the Open Multilingal Wordnet has made many wordnets accessible as a single linked wordnet, but as it used the Princeton Wordnet of English (PWN) as a pivot, it loses concepts that are not part of PWN. The technical solution to this, a central registry of concepts, as proposed in the EuroWordnet project through the InterLingual Index, has been known for many years. However, the practical issues of how to host this index and who decides what goes in remained unsolved. Inspired by current practice in the Semantic Web and the Linked Open Data community, we propose a way to solve this issue. In this paper we define the principles and protocols for contributing to the Grid. We tested them on two use cases, adding version 3.1 of the Princeton WordNet to a CILI based on 3.0 and adding the Open Dutch Wordnet, to validate the current set up. This paper aims to be a call for action that we hope will be further discussed and ultimately taken up by the whole wordnet community.

## introduction princeton wordnet (pwn @xcite ) has existed for 25 years. it is a manually created resource that has proven its worth in many different aspects of linguistics, computational linguistics, industrial applications and last but not least lexicology and knowledge engineering, cited over 11,000 times in google scholar foot_0 . it models language based on a division between words and con-cepts (represented as synsets) and semantic relations between these synsets. wordnet provided a different perspective on lexical resources from the traditional view in which the lemmas are the basis for defining concepts. since eurowordnet @xcite , the princeton wordnet model has spread to many other languages all over the world and has been extended with inter-lingual relations through the interlingual index (ili). by linking concepts across languages it became possible to compare wordnets across languages, raising fundamental issues with respect to the definition of a word and a concept. because synsets are based on sets of synonyms, they mainly represent concepts lexicalized in a particular language (although you can have a synset with a phrase rather than a single word). this implies that different language wordnets may define different concepts related to the network and in fact define semantic spaces that partially match and partially do not. within eurowordnet, two approaches were defined to build wordnets: expand and merge. the expand method takes the concepts from the princeton wordnet (pwn) as a starting point and translates the synonyms in the synsets to equivalences in the target language. if the same word is a translation of synonyms in different synsets, this creates different senses for the translation. by default, the fund of concepts for this wordnet and the semantic space is identical to the pwn structure. concepts that are not lexicalized in english cannot be represented, or will be added to the nearest possible synset, even if the denotation is slightly different. the merge method takes the words of a language as a starting point and independently creates the synsets and relations between them. this leads to an independently created semantic space, which can then be aligned with the pwn structure by providing equivalence relations. in the case of the merge approach, the spaces are usually partially aligned and there may be concepts that are in the new wordnet but not in pwn. currently, there is no central registry for these new concepts. wordnet builders for different languages have no control over the concepts included in pwn and cannot easily share their concepts to other wordnet builders. some projects have created their own internal interlingual indexes (for example mcr @xcite and the multilingual wordnet @xcite but these have not been widely adopted, are also based on pwn and most importantly cannot be modified by the community. the idea of a globalwordnet grid (gwg): a platform for making all wordnets and their linkage available was proposed at the bi-annual business meeting of the global wordnet conference in jeju, korea 2006. such a platform would enable the discussion about what defines a word and a concept across the different wordnets and also enable concept-sharing in a more fundamental way. the open multilingual wordnet (omw: @xcite went a long way to making linked wordnets available. the key insight was that wordnets could only be legally linked if the data was freely available and allowed manipulation and redistribution. they showed that wordnets were cited more if released under an open license, and managed to persuade many projects to release under open licenses. as a result there are now open wordnets available for 33 languages, all linked to each other, as well as automatically constructed data for 150 languages. they postponed the question of how to link concepts across all languages by using pwn 3.0 as a de facto ili, and dropping concepts that could not be linked. concluding: the essential problem of how to coordinate adding new concepts for multiple languages has not been realized until today. we want to start a new era for wordnets by establishing a framework so that the building and comparison of the different language wordnets may achieve another level: both theoretically and from an engineering point of view. this paper describes the details of this platform and opens up the discussion with the community how to proceed. the paper is further structured as follows. in section 2, we give the background and motivation for the grid, while section 3 describes the main principles for the gwg and section 4 for the collab-orative ili (cili). section 5 describes the procedures and the current status. in section 6, we explain how the ili is used to map to word-net3.0 and wordnet3.1. we also discuss methods for gloss-comparison across synsets in wordnets to find matches and candidates for new concepts. section 7 reports on an experiment to map the open dutch wordnet to the grid and the attempt to find new ili concepts. finally in section 8, we discuss the future options to proceed and come to our conclusions. ## background and motivation the global wordnet association website currently lists 76 wordnet groups and projects for 47 languages and other initiatives such as in-dowordnet and asian wordnet with many more languages. not all of these projects are at the stage where they have produced a working wordnet. these wordnets almost all have some relation with pwn, either through the expand method or through equivalence relations (merge). all wordnets implement the notion of a synset as the core structure with at least lexical semantic relations between these synsets. although pwn has a welldefined structure, the development of wordnets for other languages shows a large variety of decisions and choices. some of these choices relate to the content of the databases, whereas others apply to the way the resources are distributed. this variation seriously hampers the use and principled study of the wordnets, especially since it is not possible to obtain all wordnets and access them through a unified format and api, which is our main motivation for establishing the gwg platform. further, different wordnet projects have extended the wordnet structure in different ways, adding different relations and using conventions. because of this, it is hard to compare wordnets across languages. in addition to these more fundamental problems, there are also various practical problems for usage of the collection of wordnets. different wordnets are linked to different versions of the princeton wordnet, released in different formats (e.g. princeton offsets and sense-keys, euroword-net xml, multiwordnet, wordnetlmf, rdf) and according to different licenses (from completely open source to commercially restricted). further, many wordnets have added new concepts, but as there is no central ili how many of these, if any, are duplicates? when princeton releases a new version of wordnet, it immediately leads to a further decrease in compatibility of wordnets and all related tools and systems, in particular as synset identifiers cannot be preserved across versions, although sense keys are intended to be preserved. the fact that all wordnets and systems adhere to some version of the princeton wordnet also means that the fund of concepts is biased towards an anglo-saxon worldview and is not open to concepts from other languages and cultures. it could be argued that these problems would go away if a single multilingual database was developed instead. this would, in theory, solve problems of incompatible formats and coordination. in practice, however there is no single group that has expertise in all the world's languages. further, much experimentation is done in the different projects; adding new relations @xcite , adding richer domains @xcite , adding new parts-of-speech (seah and bond, 2014) and so forth. this would be harder to do in one monolithic project. as time passes, and pwn now celebrates its 25th anniversary, the need for implementing the gwg becomes more urgent. the gwg should be a platform for achieving linguistic and conceptual interoperability across wordnets and all related machinery. it should allow researchers to study the universals and idiosyncracies in lexicalisation across languages, to address fundamental questions about what is a word and what is a concept @xcite . tools built on wordnets should enable the development of software that can process text in any language according to a common semantic backbone as was demonstrated by the kyoto 2 @xcite and newsreader foot_2 @xcite projects. the projects contribute data for wordnets that they produce in an agreed upon format: word-netlmf or a lemon-based wordnetrdf. these should be validated and checked by the projects, who will have the responsibility of clearly marking which synsets are ready to be included in the ili (that is, hand checked to a good quality). although most projects specialize in a single language, there are some that produce multiple languages: both lmf and lemon can handle this. as the gwg will manipulate and redistribute the projects' data, it must be released under a suitable open license. the cili is released under a the creative commons attribution 4.0 (cc by) license. however, some projects use the share-alike license (cc by sa). in order to keep compatibility across the grid, any projects in the global wordnet grid must have a license compatible with cc by sa (such as the original wordnet license, cc by, mit and many others), and the entire grid will be released under this license. the individual projects, starting with pwn, are the foundations upon which the gwg is built, the cili links them and the platform ties them together, allows for versioning and adaptation through the community. ## the collaborative ili (cili) the collaborative ili is an extension of the ili defined in eurowordnet (see @xcite , for more details). as a base for the cili we take the synsets currently in princeton wordnet 3.0, the de facto ili for the open multilingual wordnet. this shows its central position in the current wordnet community. each synset in pwn 3.0 gives rise to a concept in the cili. the cili is just a collection of concepts to which all wordnets are linked. it does not duplicate the relations between these concepts as represented in any wordnet and it does not have any lexicalizations. concepts and concept identifiers in the cili are permanent. they will never be removed or changed. however, new concepts can be added to the cili but only if: the cili is expanded when a project commits a wordnet, or a new version of a wordnet, to the repository. a committed wordnet is analysed by the moderators of the site (the authors of this submission). if syntactically correct, we will update the ili records for all synsets that have such a record as a value of the ili-attribute so that the records get owl:sameas mappings to the contributed wordnet. all synsets without an cili-attribute that fulfill the conditions given above (linked, uniquely defined) will generate a proposed new concept which is distributed to the wordnet community for feedback and voting. gloss similarity can be used to find cili concepts that are similar, where we can limit the search space on the basis of the semantic relations (of any linked wordnet). this prevents orphan concepts to be added that cannot be positioned in the semantic space of any available wordnet. we will demonstrate this in the next sections for princeton wordnet 3.1 and the open dutch wordnet. ## the community platform the gwg platform consists of: the versioning control system is used to keep track of changes and contributions. adapting the ili within gwg is important to get a better mapping across wordnets, especially when following a merge approach. it enables us to bypass conceptual gaps in pwn and the english language and share related resources across languages such as parallel corpora, ontologies, terminologies and sense-tagged corpora. it should also tighten definitions of synonyms and relations through translation relations across texts in different languages or word embeddings derived for any language (such as @xcite . ultimately, it allows us to define what is a word and what is a concept across languages. there should be no limit to the number of concepts. phrasenets are equally legitimate as synsets to define a concept. we can allow for example for frequent adjective-noun, noun-prep-noun, verb-object combinations as well as for proverbs, idioms and compounds in languages. whether and how these concepts are lexicalized is up to the wordnet builders in each language. ultimately, we will be able to infer which and how many languages provide some type of lexicalization for these concepts. concepts that are linked to many independently-built wordnets do matter, concepts linked to a single wordnet play a minor role within the grid. the more owl:sameas relations a concept gets, the more it is valued by the wordnet community. it is also possible to axiomatize concepts through any ontology, exploiting owl:sameas relations between uris. an ontology defines a semantic space just as any other wordnet, albeit more formally. given the fact that concepts with sufficiently different glosses can be added and can be adopted by others, we can imagine that the gwg forms different layers of concepts, starting from a core of concepts shared by many wordnets, possibly ontologized and applied to many different texts in different languages, up to concepts recently added and mapped to only a single wordnet. the linkage of the data can be seen as an onion model foot_3 of concepts based on: in addition to the cili itself, we will host all public wordnets that are linked to the ili and may have provided new concepts. we extended word-netlmf @xcite with some additional attributes to support the mappings of wordnets to the cili. first of all, each synset element has an optional attribute ili for the cili-record to which the synset is connected. furthermore, the definition element has an obligatory language attribute and an optional provenance attribute to enable matching concepts. below we show a wordnetlmf example for an open dutch wordnet synset with a mapping to the cili and different definitions: one of our first checks was to ensure that the graph of the 3.1 version of pwn can be mapped to the cili (which is based on version 3.0 of pwn). this should have been a trivial case as while the synset identifiers, which are based on the offset in a the release files, are not stable between versions, the sense keys used to identify the senses in princeton wordnet should be. using this as the basis of the mapping we found that 1,796 (1.5%) of all synsets were modified between version 3.0 and 3.1 and we manually mapped these synsets. the results were as follows: in these cases, one of them (typically the one with a different definition from the one that was kept), should be marked as being superceded by the other and deprecated. in the first case, a new concept is created and no other change is necessary. in the second figure 1 : examples of changes that can be made to the cili case, two new concepts need to be created and linked to the original one, which should be deprecated. in summary, these changes should be the most common changes of the cili as it develops. deprecate a synset may be flagged as deprecated, meaning that we no longer consider it a true lexical concept. this is primarily the case when a compound term has been introduced by mistake. the synset identifier is not removed from the ili. supercede if a duplicate is detected we would choose one of the synsets to remain, and the second synset identifier is marked as deprecated and a link is introduced to the superceding synset, but this second synset is not removed from the cili. split if a synset is considered to generalize two distinct concepts we split it into two new synsets and add these as hyponyms, which are marked as supercedents of the original synset. the original synset is marked as deprecated but not removed from the ili. fork alternatively if the original synset is still considered valid it is kept undeprecated and a new more specific and closely related synset is added. note, that a new wordnet version on its own does not give enough information to decide when a concept should be deprecated or superceded. the platform must therefore allow projects to suggest this as a separate operation. ## the open dutch wordnet the open dutch wordnet @xcite al. (2016) ) was created from pwn through a mixture of expand and merge methods. pwn synset identifiers and relations have been re-used as much as possible. however, new concepts that originate from the referentie bestand nederlands (rbn: van der vliet, 2007)) and have no equivalence relation to pwn synsets have been added. the first sense is lexicalized in english (beer belly, beer gut, but has not yet been added to pwn. both the concepts are linked (as hyponyms) to existing synsets in pwn, therefore to add the concepts to the cili, the odwn project would just need to write english glosses. in total there are 21,636 synsets without a mapping to a pwn synset and therefore without a dutch english perzikhuid peach skin kalfskotelet veal chop natuurramp natural disaster verwachtingspatroon expectations sluikreclame product placement figure 2: odwn entries not in pwn 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 precision recall sultan et al. dice tf-idf mapping to the cili. from these, there are about 5,067 synsets in which case the lemma as translated by google translate is not an entry in pwn and another 4,479 synsets for which the translations have a low similarity according to the pwn hierarchy, using the method described by @xcite . we show some more examples of translations not in pwn in figure 2 . we consider these 9,546 synsets potential new cili concepts. to validate these as new, we need to ensure that they do not match an existing english gloss. this task is complicated by two main issues: firstly, semantic textual similarity is still a difficult task and secondly, we are using machine translations of the definitions, which introduces further error into the process. to investigate whether automatic methods would solve this task we translated the definitions of dutch synsets which were already aligned to synsets in pwn and attempted to see if we can distinguish this gloss from similar glosses, in particular glosses of synsets that were up to 3 hyperonym/hyponym links from the target synset. we tried three similarity metrics, namely, the dice co-efficient, the cosine of tf-idf vectors of the glosses and an alignment method @xcite , which had the strongest performance for the semantic textual similarity task at semeval-2014. for each of these methods, we varied the acceptance threshold and calculated precision and recall in the usual manner and the results are presented in figure 3 . a random baseline has an expected precision of 3.0% and the highest f-measure was 35.5%: a strong improvement. however, the performance of the semantic matching is still low, and while high recall can be achieved, which would allow us to select a list of potential duplicates this is only at very low precision, meaning that annotators may have to work through a very long list of candidates. we believe this in part due to the relatively short glosses in odwn, for example, for 'afweersystem' ('immune system'), the gloss is only 'afweer tegen ziektes' ('defense against diseases') where as the pwn gloss is 27 words long: "a system (including the thymus and bone marrow and lymphoid tissues) that protects the body from foreign substances and pathogenic organisms by producing the immune response". as such, automatic systems can aid in the detection of duplicates in the cili but must be considered along with guidelines that glosses must be submitted in english and not automatically translated and that glosses must conform to quality guidelines. our impression overall so far is that many of the odwn synsets are already in pwn, although it is very difficult in some cases to find them. the best candidates for new concepts are actually translations of synonyms that could not be found as entries in pwn (5,067 in total). however, even these need critical review and their glosses should have zero scores compared with a wide range of candidate synsets. concluding, we can say that extending the cili with new concepts should be done conservatively and with great care. ## future work and conclusions we presented the implementation of the global wordnet grid, which has been pending for many years. we described the data structures and data points as well as the main principles, the protocols and the motivation. the success of the platform will depend on the community. we described two use cases. they made it clear that the process is not trivial and we still will need to discuss many