Making a Semantic Event-type Ontology Multilingual (2022)

Abstract: We present an extension of the SynSemClass Event-type Ontology, originally conceived as a bilingual Czech-English resource. We added German entries to the classes representing the concepts of the ontology. Having a different starting point than the original work (unannotated parallel corpus without links to a valency lexicon and, of course, different existing lexical resources), it was a challenge to adapt the annotation guidelines, the data model and the tools used for the original version. We describe the process and results of working in such a setup. We also show the next steps to adapt the annotation process, data structures and formats and tools necessary to make the addition of a new language in the future more smooth and efficient, and possibly to allow for various teams to work on SynSemClass extensions to many languages concurrently. We also present the latest release which contains the results of adding German, freely available for download as well as for online access.

## introduction in natural language processing (nlp), lexical resources play an important role for supporting the computer's understanding of human language by providing gold standard data for nlp experiments and a wide range of nlp tasks and applications, such as information extraction, event extraction, sentence similarity, etc. this paper presents results of building a multilingual semantic event-type ontology called synsem-class, a linguistic resource that can be used to compare semantic and syntactic properties across languages, which provides curated data for nlp experiments with cross-lingual synonyms, such as synonym discovery, feature mapping, etc. the main purpose of our lexicon is to represent the cross-lingual meaning of the state or event expressed by the set of verbs assigned to the individual synonym classes. we believe that multilingual synonyms support deeper understanding and comparability of verb usage in different languages. our long-term aim is to create an event-type ontology that can be referenced and used as a human-readable and human-understandable database for all types of events, processes and states. having the applicability for different tasks in mind, the granularity of the synsemclass synonym classes are intermediate in granularity, between the relatively broad nature of framenet frames, and the often very fine-grained distinctions in wordnet verb senses. the contributions of this paper are as follows. we present a new workflow for extending the existing bilingual synsemclass lexicon with new languages by example of german. the re-design of the annotation workflow was necessary as the original annotations for english-czech were based on a parallel corpus with deep syntactical annotations, the prague czech-english dependency treebank, which is not available for all languages. the new workflow was designed so that the majority of steps can be applied for other languages, too, with minor modifications. we show our first results with the latest release of the lexicon which contains 153 newly added german class members based on the new annotation workflow. we describe the latest release of synsemclass v3.5 which contains the interim results of the work described here and which is freely available. 1 2 related work work related to our project concerns research on acquiring synonyms from language sources (section 2.1) and research integrating examined information from multiple sources (section 2.2). ## synsemclass lexicon the multilingual lexicon synsemclass groups synonymous meanings and structural properties of verbs into classes, each of which represents a single concept (e. g., of eating). 5 so far, we have decided to focus on verbal synonyms since they carry the key syntactic-semantic information for language understanding. as described in detail in @xcite there is no specific model or lexicographic theory behind building our database. however, the notion of synonymy used is based on the "loose" definition of synonymy by lyons and jackson @xcite , or alternatively and very closely, on both "near-synonyms" and "partial synonyms" as defined by lyons @xcite or "plesionyms" as defined by cruse @xcite . the valency theory used in the lexicon is based on the functional generative description theory @xcite . a functionally adequate relationship (regardless of language) must exist between the meanings of all verbs (called "class members," or cms) within one synonym class in synsemclass, i. e., the english, czech, and german verbs must be synonymous (at least) in some context(s), as evidenced by the corpora used. this is in line with the general approach to synonymy as described in the previous paragraph. besides semantic synonymy between the individual cms, the restrictions are also of semantic-syntactic nature: all synonym classes have a fixed set of semantic roles, and for each new cm (german or otherwise) to be added to a class, it is necessary to "fit" in this given roleset, by means of mapping the verb's syntactic arguments to the roleset. each role describes a possible concrete participant in a concrete event that is of the type defined by the class. for example, the class vec00476 absorb / pohltit, as concept of "absorbing", has two semantic roles, absorber and absorbed, and for each new cm to be added there, it must be possible, in the prototypical case, to create a mapping between its syntactic arguments and the roles in that class' roleset; see the example in our web-based lexicon (fig. 1 ), or in the editor used for annotation (fig. 2 ). 6 to have empirical evidence for such decisions, the synsemclass lexicon is being developed in a "bottomup" fashion; the first synonym classes with the en-cz cms were taken from actual examples from a parallel english-czech corpus, the prague czech-english dependency treebank (pcedt) @xcite . 7 for any extension by new entries or to a new language, we also require that corpora and existing lexicons are used to support the automatic pre-extraction of candidate words as well as the annotation decisions taken during the manual pass. ## adding german adding german synonyms to the already existing bilingual (english-czech) synonym classes was a challenge since it is the first language added to the existing lexicon that is not processed within the original internal team only. also, the input set of resources was not as rich as it was for czech: we could not build upon a parallel corpus with deep syntactic annotation like the pcedt for english-czech. several new technical challenges had to be tackled and a new workflow had to be designed. we also faced some new research questions; among the most important were: is synsemclass ready for (more) multilinguality?, can it be extended (semi-)automatically, efficiently, with what accuracy? are any changes in its structure, semantic roles, sense definitions, class hierarchy, etc. necessary to allow for multilinguality (to more concepts, more verbs to existing concepts, more languages)? from our first experiments with german in a pilot study of approximately 100 german verb roots @xcite , we learned that expanding synsemclass to include german means the completion of two tasks: to accomplish the first task and to extract german synonyms, we use an automatic aligner on a parallel corpus to extract candidate synonyms. the second task is performed by manual annotations using a tool called synonyms editor we designed for this purpose (syned) @xcite . syned allows to edit cms and the required syntactic-semantic information (mapping between semantic roles and valency arguments), add and edit links to external resources and select examples. ## results the latest release, synsemclass3.5 foot_18 , published in july 2021, contains 600 classes. of the original 56,022 cm candidates, approx. 9,000 cms remained in this lexicon version, i. e., approx. 4,630 english, 4,249 czech -and the 153 newly added german cms (see sect. 4). we consider this edition to be groundbreaking in that it contains a new language (german) which comes from another external corpus. it marks the start of making synsemclass multilingual, even if several issues still remain (cf. sect. 4.5). the resource is also available for browsing online. foot_19 as a step towards full multilinguality, it now allows users to select the language(s) whose cms to show when displaying an entry. similarly, it allows to display (only) user-selected external resources (such as framenet for english, woxikon for german, vallex for czech, etc.), in order to unclutter the display. more features will be added (such as search across languages, search by roles, etc.) as the number of languages grows. since july 2021, the lexicon has grown considerably, doubling the number of classes. from the original 70,839 cm candidates, 6,105 english, 6,037 czech, and 533 german cms (in 61 classes) are kept. the release of synsemclass version 4 is planned for early spring 2022. version 4 is also undergoing both a detailed and intensive annotation check and contains new features, such as semantic role definitions, semantic role hierarchy, (czech) aspectual verb counterparts, etc.; these additional features are however mostly unrelated to the work on german as described here (sect. 4). ## conclusions and future work we have described the process and results of the extension of the synsemclass event-type ontology to cover german. this extension did not only serve to add german verbs to the ontology, but also has helped us to understand the necessary conditions for adding another language to such a resource, and to formulate the "division of work" (and of resources and tools) between the shared, central (core or main) part of the ontology and the language-dependent parts. at the same time, we have been able to generalize the description of the resources needed for the preparation phase of adding a new language, which includes the identification of the necessary resources, including existing syntactic and semantic lexicons and sufficiently-sized parallel corpora. on the technical side, the data structure has been changed to separate the language-dependent data in a stand-off fashion, and the editor has been updated and enhanced to reflect this change. the dataset (version 4 of synsemclass) will be published soon, as will the editor and related specifications. for the future, we plan to expand on the work described here in several directions. first, we have already started adding spanish, and we hope that after that, we will be able to assemble a larger group of interested teams to work on more languages in parallel, either from scratch or by converting other similar resources and updating them according to the synsem-class specifications. we chose paracrawl foot_20 because it is the largest resource, and it is constantly being developed and more languages are added (in version 9 from sept. 2021, paracrawl provides corpora for over 40 language-pairs). therefore, we (or anyone interested) can easily expand synsemclass to other languages by adopting our data preparation steps as developed for the extension to german. at the same time, we plan to enrich the synsemclass specification in several respects -across all languages, or more precisely, in the language-independent core part: add definitions/descriptions to all semantic roles used and later to all classes and add hierarchy (also to both roles and classes). in the language-specific part, we are working on providing (automated) tools for expanding the coverage on a large scale (using large contextual language models), adding nouns and adjectives expressing the concept in syntactically different ways, and enhancing the web browsing and searching functionality for the resulting lexicon. also, we plan to publish separately the more theoretical lexicalsemantic considerations, findings and comparisons that arose during the so far rather bottom-up approach that has not been driven, in the core questions, by any existing theoretical framework. it should also be mentioned that the project is part of a larger early-stage project for multilingual knowledge representation, where the synsemclass entries (classes) will serve as a grounding (of sorts) for all events and states in that representation, connecting (relating) all other entities in the resulting representation which will also be grounded (by other means). while some verb annotation experiments have been done for the previous versions of synsemclass, the full specification is still to be developed.