Linked Open Data compliant Representation of the Interlinking of N ordic Wordnets and Sign Language Data (2023)

Abstract: We present ongoing work dealing with a Linked Open Data (LOD) compliant representation of Sign Language (SL) data, with the goal of supporting the cross-lingual linking of SL data, also to Spoken Language data. As the European EASIER research project has already investigated the use of Open Multilingual Wordnet (OMW) datasets for cross-linking German and Greek SL data, we propose a unified RDF-based representation of OMW and SL data. In this context, we experimented with the transformation into RDF of a rich dataset, which links Danish Sign Language data and the wordnet for Danish, DanNet. We extend this work to other Nordic languages, aiming at supporting cross-lingual comparisons of Nordic Sign Languages. This unified formal representation offers a semantic repository of information on SL data that could be accessed for supporting the creation of datasets for training or evaluating NLP applications that involve SLs.

## introduction we present work that builds on top of an approach consisting in using wordnets for interlinking german and greek sign language (sl) data, as described in @xcite . this approach makes use of shared ids of the open multilingual wordnet (omw) @xcite @xcite infrastructure as a base for interlinking the two sl datasets. as a first step of our work dealing with the interlinking of nordic wordnets and sl data, we investigated the work described in @xcite , which is discussing the use of the danish wordnet, dannet @xcite , for adding relevant danish equivalents to each sign that is already annotated with some sl glosses or words. we were happy to get access to the whole danish dataset that lists more than 2000 sign entries, which include sl glosses, transcriptions, links to videos, associated lemmas, synonyms, english translations, dannet ids, etc. (see section 4.1). we could already port a number of elements of this danish dataset onto a linked data compliant representation (see section 4.2), following our first transformation experiments, which were made with the greek and german datasets made available by the easier project. 1 we are currently extending this approach to the interlinking across nordic sls data, starting with the integration of the corresponding nordic wordnet datasets, for which @xcite gives a detailed discussion, also on the way they differ. a general overview of nordic sign languages is given in @xcite , while a comparison of the icelandic and the danish sign languages is proposed in @xcite . our work is anchored in the context of an initiative aiming at representing and publishing sign language datasets in the linguistic linked data (llod) cloud @xcite , which is a subset of the linked data (ld) cloud. 2 we can observe that sl data are not represented by datasets currently included in the llod cloud. and looking at the "overview of datasets for the sign languages of europe" published by the "easier" european project @xcite 3 we do not see any mention of a dataset being available in a linked data compliant format. the prerequisite for publishing linguistic data in the llod is to have it formally represented within the resource description framework (rdf). 4 and as a de facto standard for representing lexical information in rdf, the ontolex-lemon specifications (mccrae et al., 2017), foot_4 already exists, we investigate as a first step the (possibly partial) re-use of those specifications in order to accommodate the description and the publication of sign language datasets in the llod. figure 1 displays the core module of ontolex-lemon, which we already applied while dealing with the rdf representation of the 2 datasets made available by the easier project. ## the open multilingual wordnet (omw) infrastructure the motivation behind the open multilingual wordnet (omw) initiative @xcite @xcite is to ease the use of word-nets in multiple languages. omw proposes a shared format for supporting the interlinking of language-specific wordnets. version 1 of omw foot_7 offers 28 wordnets, foot_8 all linked to the princeton wordnet of english (pwn) @xcite , foot_9 which functions thus as a pivot wordnet for establishing links between all the other wordnets included in omw (version 1). datasets for 5 nordic languages are included in omw: danish, finnish, norwegian (nynorsk and bokmål), and swedish. 11 we also have access to the icelandic wordnet, icewordnet, which is stored at different sites. 12 the fact that these wordnets are (sometimes only partially) linked to the 5000 core word senses in princeton word-net (boyd-graber et al., 2006), foot_12 makes the interlinking of these wordnets much easier. a very helpful feature of omw version 1 is given by its online search facility, where one can type a word and gets all the related pwn synsets. 15 searching, for example, for the word "protection" we get 7 synsets returned. focusing on the synset 00817680-n, with the english lemma "protection" and the princeton wordnet gloss "the activity of protecting someone or something", we get the (linked) omw lemmas for the nordic languages, as presented in in some cases the transcription can be either semi-automatically generated or produced by human transcribers with different skills and views on which phonological elements of a sign should be transcribed. @xcite , for example, report in their experiment that the similarity (based on measuring levenshtein distance) of transcriptions provided by two undergraduate research as-sistants, working in a related project, was 0.69. besides this point, we observe that different sl datasets are transcribed with different transcription systems, e.g. hamnosys, @xcite sign-writing, @xcite or others, as is the case for the swedish sign language data 17 or the irish sign language @xcite . 18 . this issue of plurality of transcription systems makes it nearly impossible to establish a crosslinking of sl data on the basis of only those transcriptions. ## the danish data and its transformation into rdf we describe in this section in some details first the danish dataset we received from a designer 19 of the dictionary of danish signs, 20 the building of which is described in @xcite . we present then the current state of the transformation of the danish dataset onto rdf and ontolex-lemon. ## a first extension to other nordic sign languages we describe in this section first steps towards an extension of our approach to other nordic sign languages. we could already start integrating a larger number of nordic languages in our infrastructure, when considering the omw and other sources for language specific wordnet datasets, as can be seen for the concept "potential, possible" (with omw id "00044353-a") in figure 3 . we can see in figure 3 some differences in the way language data are associated with wordnet concepts. for the danish case, we need to stress, that we have therefore only one lemma, as we extract the information from the danish dataset presented in section 4.1, and there mostly only unique senses are associated with a gloss or a omw id. if we would have taken the full dannet as the source, we would have retrieved all the lemmas associated with the corresponding synset. we have now 111,166 synsets in our infrastructure, as we have been porting to rdf also the finnish wordnet included in omw, and which is not limited to the core wordnet. an additional advantage of having a unified rdf and ontolex-lexicon of all those different wordnets, is that we can easily query the resulting triple store. we use for this sparql foot_17 queries, and figure 4 shows a very basic query example. figure 4 : a very simple sparql query delivering the wordnet lemmas included in our rdf representation. in this example, the lemmas associated with the omw-id "02933842-n" this simple sparql query shows how we can find the lemmas for nordic (and other languages) associated with the omw ids we have already in our rdf-based infrastructure. we used those lemmas for getting a first access to glosses and videos available for the icelandic and the swedish sls. for icelandic, we consulted for now the icelandic signwiki, available at https://is.signwiki . org/index.php/ and for swedish, we consulted the swedish sign language dictionary, described in @xcite , and available at https: //teckensprakslexikon.su.se . next step in our work will be to establish the needed cooperation with the maintainers of those sites. ## conclusions and future work our transformation work resulted in a harmonised representation of data from both spoken and sign languages that was originally stored in different formats in different locations and in different formats. taking advantage of the work proposed by @xcite and ( troelsgård and kristoffersen, 2018 we started to expand our work to other nordic languages. we already integrated finnish, icelandic, norwegian (nynorsk and bokmål) and swedish in the rdf and ontolex-lemon representation of wordnet data. we observed that for those languages, there are sl datasets and interactive portals available. it will be more challenging to expand to nordic languages with fewer digital resources, such as faroese, greenlandic and sami, which to our knowledge have no wordnets yet, but we are aware of, for example, a portal for the faroese sl ( https://fo.signwiki.org/index.php/b% c3%b3lkur:or%c3%b0ab%c3%b3k_a-%c3%98). we might be able to use the experience gained in this work as a point of departure for working on other low resourced languages, like maltese or slovak, as we are involved in related projects, but which are not primarily dealing with sls. we hope to create this way a semantically organised repository of cross-lingual (both sls and spoken language data) data in the field of lowresource sign languages, which can be of help for supporting the creation of datasets for training or evaluating nlp applications, thinking in the first place at automated translation.