Annotation Issues in U niversal D ependencies for K orean and J apanese (2020)

Abstract: To investigate issues that arise in the process of developing a Universal Dependency (UD) treebank for Korean and Japanese, we begin by addressing the typological characteristics of Korean and Japanese. Both Korean and Japanese are agglutinative and head-final languages. And the principle of word segmentation for both languages is different from English, which makes it difficult to apply UD guidelines. Following the typological characteristics of the two languages and the issue of UD application, we review the application of UPOS and DEPREL schemes to the two languages. The annotation principles for AUX, ADJ, DET, ADP and PART are discussed for the UPOS scheme, and the annotation principles for case, aux, iobj, and obl are discussed for the DEPREL scheme.

## introduction this article investigates issues arising in the process of building a universal dependency (ud) treebank for korean and japanese. the two languages possess similarities in typology. korean and japanese as a language have in common: sov (subject-object-verb) word order and agglutination. in the design principles presented by the ud project, the principles do not conform to the characteristics of agglutinative languages. the following are part of design principles presented in the ud project: for the korean language, it is challenging to satisfy design principles 1 and 2. @xcite conducted a study on measuring cross-linguistic complexity using ud language resources. for a total of 37 languages, the study analyzes linguistic complexity utilizing a given measurement framework for morphological and syntactic complexity. in the provided measurement framework, morphological complexity has eight complexity variations that include ttr (type-token ratio) and syntactic complexity has seven complexity variations that include cr_posp (diversity of pos bi-gram). the results indicate that measures of syntactic complexity might be on average less robust than those of morphological complexity. unfortunately, the language analysis unit for korean and japanese were deemed too difficult and were excluded from this study. in ud annotation scheme, the part-of-speech (pos) analysis results created a language specific part-of-speech layer (xpos) field in addition to upos that exposes the characteristics within the individual languages. however, it is not easy nor ideal to apply the ud scheme created for an inflected language where the content and functional words are clearly separated by word dividing whitespaces, directly onto an agglutinative language in which functional words are integrated with the content word to form a single unit such as a word or an eojeol. in this study, we examine the problem of how ud is applied to agglutinative languages and morphologically rich languages. ## typological characteristics of korean and japanese since ud was designed primarily for inflected languages, such as english, it is difficult to apply it directly onto the korean language which is an agglutinative language. characteristic to agglutinative languages, korean is highly developed in postpositions and verbal endings. this is a major stumbling block to the application of ud to the korean language. these problems are present not only in korean but also in japanese. therefore, it is necessary to compare and analyze the application patterns of ud in korean and japanese. the following characteristics are mentioned as typological features of the korean language, but also applies to the japanese language: the korean and japanese languages are both agglutinative languages and also commonly follow a sov word order.(sohn, 2001) furthermore, as the most distinctive feature of languages with a sov word order, such as korean and japanese, the two languages are rich in postpositions and verbal endings. this preceding nature is one of the key differences compared to english and other languages where functional words with grammatical functions are placed in front of the content word. in terms of the location of head directionality, korean and japanese place the head on the right-hand side from the existing parsing resources, which is characteristic to head-final languages @xcite . in english, which is the standard for stanford dependencies, places the head on the left-hand side. in other words, the location of the head in coordinate structures for english is different from languages such as korean or japanese. in korean and japanese, the head usually appears on the right-hand side, so if the coordinate or parallel elements are annotated, the root is assigned to the right-hand element according to the head-final principle. to prevent this confusion, establishment of principles addressing this issue is in dire need. figure 1 is an example of the annotation of conj, the relation label between two elements connected by a coordinating conjunction. in both korean and japanese, there is a form of postposition(called particle in japanese) and verbal endings. these represent grammatical relations among the content words. in the correlating japanese component, the categories "particle(case):" and "particle(phrase_final)" are included in the part-of-speech, while only "case postpositions" is included in the korean part-of-speech. in the korean component, case postpositions are generally accepted as words, but verbal endings are not considered within the category of a "word." this is because words are achieved only when combined with a verbal stem. some of the endings in korean correspond to the particle(case) in japanese and some mapping to the particle(phrase_final). compared to the other part-of-speech with relatively clear boundaries and clear lexical meanings, postposition and verbal ending are one cause of difficulties in assigning ud annotation labels to both languages. the boundaries are not only vague, but also carry stronger grammatical meanings as opposed to lexical meanings. ## conclusion we reviewed the application of the ud scheme to the korean and japanese treebanks as we identified and discussed the areas that require awareness of when constructing a ud treebank for an agglutinative language. we identified issues that arise when determining the basic units and in applying upos and deprel schemes. for the upos scheme, issues related to applying aux, adj, postposition, and verbal ending were addressed. for the deprel scheme, the application and usage of case, aux, and iobj labels are discussed. the above discussions will be essential in establishing standards for building or improving ud treebanks in agglutinative languages in the future. this review of the current state of ud treebanks for agglutinative languages discloses a need for a ud treebank that better reflects the unique characteristics of the language for construction. pkt was revised to further reflect the unique characteristics of the korean language by modifying upos and deprel in reference to the korean xpos @xcite . but still, the basic unit for analysis is a word unit, which does not capture all the syntactic functions of postpositions or verbal endings. the japanese ud makes better use of its unique characteristics than the korean ud in the sense that it uses its own units. however, as we can see from the application of iobj that there is still much room for improvement. the ud scheme is evolving through continuous research and workshops. as a result, ud treebanks are also becoming more diverse. this study focused on korean and japanese to examine the characteristics of agglutinative languages, but the other languages such as turkish did not explain together, which is left as future work. we hope that this article will contribute to the vitalization of discussions on agglutinative languages.