I ndo M orph: a Morphology Engine for I ndonesian (2025)

Abstract: Indonesian is an agglutinative language and rich in morphology. Although it has more than 250 million speakers, it is a low resource language in NLP field. Many Indonesian NLP resources are scattered, undocumented, and not publicly available. In this paper we address the issue of analyzing morphology as well as generating Indonesian words. We introduce IndoMorph, a morphology analyzer and word generator for Indonesian. In an agglutinative language, morphology deconstruction can be crucial to understand the structure and meaning of words. IndoMorph can be useful for language modeling and testing certain analyses. In addition, it can be employed to make a new Indonesian subword representation resource such as Indonesian morphology dictionary (IMD), used as a language education tool, or embedded in various applications such as text analysis applications. We hope that IndoMorph can be employed not only in the Indonesian NLP research development, but also in the NLP research of any agglutinative languages.

## introduction indonesian, called bahasa indonesia (lit. 'the language of indonesia') by its speakers, is a western malayo-polynesian language of the austronesian language family. within this subgroup, it belongs to the malayic branch, which includes standard malay spoken in malaysia. the indonesian language is over 80% cognate with standard malay (eberhard et al., 2023). it is spoken mainly in the republic of indonesia as the official and national language. around 43 million people speak indonesian as their first language and more than 156 million people speak indonesian as their second language (2010 census data). although it is the most spoken austronesian language, it is considered as a low resource language in nlp (cahyawijaya et al., 2023). morphologically, indonesian is a mildly agglutinative language compared to finnish or turkish, where the morpheme-per-word ratio is higher (larasati et al., 2011). this paper describes indomorph, a morphology analyzer and word generator for indonesian, a low resource language in nlp field. in section 2, we discuss indonesian morphology, followed by a brief introduction of previous research on indonesian morphology in nlp in section 3. section 4 presents our work, we describe the dataset and the logic of indomorph. section 5 mentions the usage and future development of indomorph as well as the results of some evaluations we carried out on indomorph. finally, section 6 concludes. ## indonesian morphology word-formation in indonesian involves affixation, cliticization, reduplication, compounding, and abbreviation (kridalaksana, 1989). in indomorph, we mainly deal with rules of affixation, cliticization, and reduplication since they are very complex. indonesian has a rich affixation system, including a variety of prefixes, suffixes, and circumfixes. @xcite most of the affixes in indonesian are derivational (sneddon et al., 2012). prefixes such as men-, di-, ber-, ter-, pen-, per-, ke-, and seprecede the base form. suffixes such as -kan, -i, and -an follow the base form. circumfixes such as ke-...-an, pen-...an, per-...-an, and se-...-nya wrap around the base form. when affixes combine with base forms, several phonetic or phonological alternations through morphophonemic processes occur. a number of sound changes occur when menor pencombines with a base form. a base loses its initial consonant if the consonant is one of the following voiceless consonants: p, t, s, and k. it retains its initial consonant otherwise. in addition, when the base consists of only one syllable, menbecomes mengeand penbecomes pengewith no sound changes in the base. the details of these morphophonemic are described in reference grammars and papers (sneddon et al., 2012; moeljadi et al., 2015). indonesian has two types of clitics: proclitics and enclitics. proclitics, such as kuand kau-, precedes words, included affixed words. enclitics, such as -ku, -mu, and -nya follows words, included affixed words. in addition to affixes and clitics, there are particles -lah and -kah which behave similarly as suffixes. in indomorph, proclitics are regarded as prefixes and enclitics as well as particles are regarded as suffixes. we analyze all combinations of possible prefixes such as se-+ber-, ter-+ke-, and ber-+se-+pen-; all combinations of possible suffixes such as -an+-i; all combinations of prefixes and suffixes such as men-+-kan and di-+-i; as well as all combinations of affixes, clitics, and particles such as ku-+men-, -kan+-mu, -ku+-kah, and -an+-nya+-lah. indonesian has four types of reduplication: full reduplication, partial reduplication, imitative reduplication, and affixed reduplication (denistia and baayen, 2022). in full reduplication, the entire base form is repeated, e.g. buku-buku 'books' from the base buku 'book'. in partial reduplication, only part of the base form is repeated, e.g. beberapa 'several' from the base berapa 'how many/much'. in imitative reduplication, some consonants and vowels in the base form change, e.g. sayur-mayur various kinds of vegetables' from the base sayur 'vegetable' and gerak-gerik 'various movements' from the base gerak 'movement'. in indomorph, words having partial reduplication and imitative reduplication are listed in the dataset since the number is fixed and not productive. there is also affixed reduplication, which involves adding affixes to reduplicated base forms. there are three types of affixed reduplication depending on the position of the affixed form: in addition to these four types of reduplication, there are reduplication with infixes such as gunung-gemunung 'various mountains' from the base gunung 'mountain', affixed imitative reduplication such as bercoreng-moreng from the base coreng, and triplication such as dar-der-dor from the base dor. the number of these types of reduplication is limited, thus they are all listed in the dataset of indomorph. we address these issues we found in the previous research, thus we analyze all affixes, clitics, and all possible combinations of affixes, clitics, and reduplication in indomorph. ## indomorph features this section describes the dataset and the logic of indomorph: forward morphology (generator) and inverse morphology (analyzer), as well as formation candidate making. ## conclusion in this paper, we have shown our contribution in dealing with the complex morphology of indonesian, a low-resource language in nlp, by presenting indomorph. we begin by showing the dataset we use for indomorph, mainly consists of lists of supporting words/phonemes and morphology rules. we then explain how the dataset is used to perform forward morphology (generator) and inverse morphology (analyzer) for various cases. we continue by presenting the current usages of the indomorph as a tool to find correct indonesian word formation, to show the formation with clarity and interpretability, and to find error morphological patterns. in the future, we plan to improve indomorph to recognize more minor cases, as a supporting tool for creating indonesian morphology dictionary, to implement machine learning, to have internal validation mechanism, and to encompass more agglutinative languages, evolving indomorph to agglumorph.