A Four-Dialect Treebank for O ccitan: Building Process and Parsing Experiments (2020)

Abstract: Occitan is a Romance language spoken mainly in the south of France. It has no official status in the country, it is not standardized and displays important diatopic variation resulting in a rich system of dialects. Recently, a first treebank for this language was created. However, this corpus is based exclusively on texts in the Lengadocian dialect. Our paper describes the work aimed at extending the existing corpus with content in three new dialects, namely Gascon, Provençau and Lemosin. We describe both the annotation of initial content in these new varieties of Occitan and experiments allowing us to identify the most efficient method for further enrichment of the corpus. We observe that parsing models trained on Occitan dialects achieve better results than a delexicalized model trained on other Romance languages despite the latter training corpus being much larger (20K vs 900K tokens). The results of the native Occitan models show an important impact of cross-dialectal lexical variation, whereas syntactic variation seems to affect the systems less. We hope that the resulting corpus, incorporating several Occitan varieties, will facilitate the training of robust NLP tools, capable of processing all kinds of Occitan texts.

## introduction occitan is a romance language spoken in southern france (except in the basque and catalan areas), in several valleys of the italian piedmont and in the val d'aran in spain. it does not have the status of an official language, and as many such languages, it is not standardized. it displays a rich system of diatopic varieties, organized into dialects. the variation can be appreciated at all levels of linguistic structure: it can be lexical or phonetic, but also morphological and syntactical (see section 2). also, there are two different spelling norms in use today, one called the classical, based on the occitan troubadours' medieval spelling, and the other closer to the french language conventions @xcite . since all these factors contribute to data sparsity, they make occitan particularly challenging for natural language processing (hereafter nlp). in fact, occitan is still relatively low-resourced, although recent efforts have started to remedy this situation. the firsts of them was the creation of the batel òc text base @xcite and the restaure project, which resulted in the creation this work is licensed under a creative commons attribution 4.0 international licence. licence details: http:// creativecommons.org/licenses/by/4.0/ . in section 2, we give a brief description of the linguistic properties of occitan and of its main dialects. section 3 describes the addition of three new dialects to the existing treebank and the resulting corpus. section 4 is dedicated to experiments looking to identify the most effective method for training a robust parsing model for all occitan dialects in the corpus. finally, in section 5, we give our conclusions and directions for future work. ## occitan: main linguistic properties and diatopic variation occitan belongs to the gallo-romance group of romance languages, together with standard french and "langues d'oïl", francoprovenc ¸al and catalan. it is closer to catalan than to french and forms with catalan a subgroup called occitano-roman @xcite . it is a null subject language with tense, person and number inflection marks on finite verbs for each person. many dialects mark number and gender inflection on all components of the noun phrase. unlike contemporary french, occitan maintains the use of the preterite (passat simple), which contrasts with the perfect tense (passat compausat), and the use of the imperfect subjunctive, even in oral colloquial speech. an example in lengadocian illustrating some of these properties is given in example 1. vos vòli pas espaurugar amb lo rescalfament planetari you.acc.pl want.1sg neg frighten with the.sg.m warming planetary.sg.m root obj advmod xcomp obl case det amod 'i don't want to scare you with global warming.' as mentioned above, occitan has several diatopic varieties, organized into dialects. the most widely accepted classification proposed by @xcite includes auvernhat, gascon, lengadocian, lemosin, provenc ¸au and vivaroaupenc (see figure 1 ), but these dialects are not homogeneous: they form a continuum with areas of greater or lesser variation. in this article we focus on four of them: lengadocian, gascon, provenc ¸au and lemosin foot_1 , since they are the ones for which the greatest number and variety of texts are currently available. differences in dialects can be appreciated at different levels (lexical, phonological, morphological and syntactical), as shown below. the variation can be lexical: e.g., the word potato translates as mandòrra in some gascon varieties, but as trufa/trufet or patana/patanon in lengadocian. a large part of this type of variation stems from different phonological processes, many of which appear in gascon: the aspirated h in word-initial position in figure 1 : occitan dialects map words such as hilh 'son', hèsta 'celebration' (cf. filh in lengadocian and lemosin, fiu in provenc ¸au and vivaroaupenc, fèsta in lengadocian and provenc ¸au, festa in lemosin, auvernhàt and vivaroaupenc), the drop of the intervocalic n in words such as lua 'moon' (cf. luna in lengadocian) and the r metathesis in words such as craba 'goat', dromir 'to sleep' (cf. respectively cabra, dormir/durmir in a large part of the lengadocian area). it is also caused by the existence of several spelling norms. since the 19th century, two major spelling conventions can be distinguished: the first was influenced by french; the second, called the "classical spelling" and inspired by the medieval troubadour spelling, appeared in the 20th century. the latter is a unified spelling convention distributed across all of the occitan territories @xcite . on the morpho-syntactic level, verb inflection varies from one dialect to another as illustrated in number person gascon lemosin lengadocian provenc ¸au sg 1st soi sei soi siáu 2nd ès ses ès/siás siás 3rd ei/es es es es pl 1st èm sem sèm siam 2nd ètz setz sètz siatz 3rd son son son son when it comes to syntax, there is more homogeneity across dialects, but gascon exhibits several important specificities. first, it has enunciative particles which mark the sentence modality: the most frequent are que for affirmative sentences, be and ja for exclamative sentences and e for interrogative sentences and subordinate clauses. they appear between the subject and the verb and their presence is even obligatory in some gascon areas. they have no equivalent in the lengadocian, provenc ¸au and lemosin dialects (cf. example 2.a). the interrogative and relative pronoun qui 'who'(cf. example 2.b), which is scarcely used in lengadocian, provenc ¸au and lemosin and only as an interrogative pronoun, has many functions in gascon, such as the subject or direct object functions (where the other dialects use que), and it can be precedeed by the preposition de regardless of the verbal rection (cf. example 2.c), which does not occur in other dialects. qui and de qui can also be a subordinating conjunction introducing a completive clause. furthermore, object clitics and reflexive pronouns are more often found in post-verbal position than it is the case in lengadocian, in which they are typically pre-verbal (cf. example 2.d). finally, unlike in other dialects, there are no indefinite or partitive articles in gascon (cf. example 2.e). lo vent que s' èra lhevat e que hasó drin fresc. the.sg.m wind part refl was risen and part did slightly cold 'the wind had started blowing and it was a bit cold.' leng.:'lo vent s'èra levat e fasiá un pauc freg.' b. l' atge qui a the age that has lit. 'the age he has', 'his age' leng.:'l'atge qu'as / que as' c. los guardians d' un concèpte de civilizacion de qui calèva preservar the.pl.m guardians of a.m.sg concept of civilization prep which ought preserve 'the guardians of a concept of civilization that needed to be preserved' leng.:'los gardians d'un concèpte de civilizacion que caliá preservar' d. ne cau pas està 's darrèr mieidia neg ought neg stay refl after noon 'you shouldn't stay after noon' leng.:'vos cal pas demorar après miègjorn' e. entà véner ø objècts de pietat. in.order.to sell objects of piety it is important to note the potential impact of these characteristics on nlp tools based on machine learning. the lexical and morpho-syntactical variation is potentially problematic, but it is mostly a question of coverage: it can be alleviated either by a carefully engineered training corpus, representative of as many dialects as possible, or by an extensive, dialect-diversified lexicon. if a combination of the two were available, we could reasonably suppose that the effect of the variation would be minimized and that a tool trained and used in such conditions would be able to pos-tag, lemmatize and parse texts independently of dialect. however, the syntactic variation has a potentially more profound effect: a gascon corpus can be expected to have more ambiguity related to relative pronouns, but also a different distribution of pos tags (i.e., more particles, fewer determiners) and of syntactic structures (i.e., more right-branching verb dependents) than corpora in other dialects. this could compromise the transfer of parsers trained on other dialects to gascon and vice versa. ## conclusion in this paper we presented an extension of an existing occitan treebank based on the lengadocian dialect with content in three additional dialects, namely gascon, lemosin and provenc ¸au. the resulting corpus contains 25k tokens, it is annotated following universal dependencies guidelines and will be made available as part of the november 2020 release. our experiments in parsing show that parsing models trained on dialects of occitan achieve better results than a delexicalized model trained on ud corpora of romance languages even though the latter is much larger (20k vs 900k tokens). this underlines once again the need to foster development of corpora for low-resourced languages: our results indicate that even a small amount of data in the target language can be expected to yield important improvements. we also observe that delexicalized models trained on occitan dialects perform better than their lexicalized counterparts. while this is in line with the observed degree of lexical variation across occitan dialects, it remains to be confirmed on larger amounts of data. on the other hand, contrary to our expectations, the syntactic variation observed in gascon did not seem to overly affect the models' performance. the most useful model across the board was the delexicalized model trained on a combination of lengadocian and gascon content. thanks to these experiments, we will be able to continue our work on corpus enrichment using a more efficient parsing model. hopefully, this will further simplify the work of human annotators and allow for faster and easier additions to the treebank, ultimately leading to the creation of robust parsing models capable of processing all occitan texts.