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# A morpheme-based treebank for Gbaya, an Ubanguian language of Central Africa

Paulette Roulon-Doko, Sylvain Kahane, Bruno Guillaume

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Paulette Roulon-Doko, Sylvain Kahane, Bruno Guillaume. A morpheme-based treebank for Gbaya, an Ubanguian language of Central Africa. Depling, SyntaxFest 2025 - Eighth International Conference on Dependency Linguistics, Aug 2025, Ljubljana, Slovenia. pp.93–102. hal-05404227

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# A morpheme-based treebank for Gbaya, an Ubanguian language of Central Africa

Paulette Roulon-Doko

CNRS, LLACAN, France
paulette.roulon@cnrs.fr

Sylvain Kahane

Paris Nanterre University,
CNRS, MoDyCo, France

Bruno Guillaume

Université de Lorraine,
CNRS, Inria, LORIA, France

Institut Universitaire de France Bruno.Guillaume@inria.fr
sylvain@kahane.fr

## Abstract

In this paper, we present the first treebank for Gbaya, a language from the under-resourced Niger-Congo family. The language has a rich system of tonal morphemes and virtually no affixes. The dependency analysis is based on a morpheme-based tokenisation and the treebank is also distributed in a word-based Universal Dependencies version. Several constructions are discussed in the paper: genitive construction, clause coordination, sentence particles, adverbial and relative clauses, serial verb constructions, reported speech, topicalization, and focalization.

## 1 Introduction

This paper presents the first treebank for a Gbaya language. We have decided to follow the tokenization proposed by Roulon-Doko (1995). In this previous work, the analysis considers many tones as autonomous units that combine with root lexical tonal pattern for grammatical reasons; there are called grammatical tones (Hyman, 2016; Rolle, 2018). These tones are placed after the determined term. In the case of verbs without lexical tonal pattern, the tone is attached to the verb base and is therefore always indicated beforehand. In order to encode this tokenization level, we use the mSUD framework (Guillaume et al., 2024). mSUD was designed for morpheme-based level annotation; it is a variant of the Surface Syntactic Universal Dependencies (SUD) (Gerdes et al., 2018a) annotation schema.<fnref n="1" /> In this paper, we will used the term “morpheme” also for units that represent tones. We will consider three kind os tokens: roots, clitics, and inflectional morphemes (which are mainly tonal tokens).

The corpus is also available<fnref n="2" /> in the Universal Dependencies (UD) framework (de Marneffe et al., 2021). To meet the UD tokenisation requirements, we provide automatic conversion to the UD format, in which tones are not expressed as separate tokens.

The corpus is made up of three tales. The tales in Gbaya are a repertoire without specialists. The language used to tell tales is the language of everyday life, with no stylistic form of its own. The storyteller, whether male or female, young or old, takes the floor spontaneously during a storytelling session. These three tales were recorded in 1970 in the village of Ndongué (Central African Republic) during traditional storytelling evenings by Paulette Roulon. Tale T16-C6, which tells the story of the woman fishing at the dam whose baby was swept away by the water after the dam burst, opened the session. It was told by Anna Zàngé, a woman in her forties. This was followed by tale T9-C7, which tells the story of the brother and sister who went on a hunting camp, which was then told by Yvonne Yàì-sò a young girl of around 17. Tale T24-C59, which tells the story of Wanto and the little cob, was told at another session by Hélène Dúì, a young woman in her thirties. The Table 1 gives an overview of the length of each tale in the treebank mSUD_Northwest_Gbaya-Autogramm.

Northwest Gbaya (ISO: GYA, WALS: gbk, Glototcode: nort2775) is part of the main linguistic group Gbaya-Mandja-Ngbaka, an Ubangian language family (a branch of the Niger-Congo phylogeny, Adamawa Ubangi). It is spoken in the northwest of the Central African Republic (CAR) and in the central-eastern part of Cameroon. It is subdivided in six dialects: four in CAR [fòdòè, fòkpàn, fòpìnà, fùgùì], usually named Gbaya-kara, and two in Cameroon [fòya, yàáyùwèè]. In

<footnote n="1">¹The mSUD corpus is available at https://github.com/surfacesyntacticud/mSUD_Northwest_Gbaya-Autogramm.</footnote>

<footnote n="2">²https://github.com/UniversalDependencies/UD_Northwest_Gbaya-Autogramm</footnote>
<table><caption>Table 1: Sizes of the 3 samples of the corpus mSUD_Northwest_Gbaya-Autogramm (version 2.15).</caption><thead><tr><th></th><th>audio length</th><th># of sentences</th><th># tokens<br>(morph-based)</th><th># tokens<br>(word-based)</th></tr></thead><tbody><tr><td>T16-C6</td><td>321s</td><td>143</td><td>1,363</td><td>847</td></tr><tr><td>T9-C7</td><td>178s</td><td>79</td><td>820</td><td>503</td></tr><tr><td>T24-C59</td><td>359s</td><td>181</td><td>1,621</td><td>1,067</td></tr><tr><td><strong>TOTAL</strong></td><td><strong>858s</strong></td><td><strong>403</strong></td><td><strong>3,804</strong></td><td><strong>2,417</strong></td></tr></tbody></table>

1996, there were 265,000 speakers: 200,000 in the western part of CAR and 65,000 in the central-eastern part of Cameroon. This paper deals with the Gbáyá ßòdòè, a Northwest Gbaya dialect spoken in Central African Republic. The annotation is based on a dictionary from Roulon-Doko (2008) and a complete grammar, based on a 4h50 oral corpus of spontaneous speaking, collected in the field between 1970 and 2013, processed with Toolbox and Elan, glossed and translated into French, by Roulon-Doko.

The consonant system has three glottalized consonants (ð, d, ʔ), four labio-velars (kp, gb, ngb, ɲm), oral consonants (both voiceless and voiced) and a complete range of nasals and semi-nasals. There are seven oral and five nasal vowels. Gbaya is a tonal language with two levels and four tones (H, L, LH, HL). All vowels carry a tone. Gbaya syllabic structure includes open and closed syllables, but no initial vowel.

Gbaya is an isolating language with very little morphology and no agreement at all. Gbaya relies minimally on derivation but makes strong use of compounding, marked in writing by a hyphen between components (e.g. gɛ́ɛ́-fɪò ceremony sp.), which is also used for adjectives-adverbs with a reduplicated structure (e.g. bàdàm-bàdàm irregularly arranged).

The lexemes are thus simple, compound, or structurally reduplicated. They are distributed across 18 categories (Roulon-Doko, 2008). Gbaya has verbs, non-verbal predicates, nouns and four subcategories of adjectives. The main lexical categories, VERB (10%), NOUN (50%), and ADJ (32.6%), have unrelated lexical stocks. For nouns, composition is very important (47.6%) and derivation very little used (3.7%).

Word order is very strict. Gbaya is an SVO language, that also makes use of non-verbal predication. The subject is compulsory, except for some construction that will be described below.

In Section 2, we explain how the tone system

is encoded as “morphemes” in the mSUD framework. The Section 3 describes the principles used for defining the maximal units. Several interesting contructions of Gbaya are described in Section 4, together with the proposed analysis in the treebank. The last Section 5 is dedicated to the conversion to the UD treebank.

## 2 The morpheme-based annotation

Verb inflection in Gbaya is marked by tone alternations, possibly accompanied by affixes. Verbal lexemes have no lexical tonal pattern, the tonal pattern they carry systematically comes from the TAM marker and is identical for all. The TAM verbal system is organized in three moods (Realis, Virtual and Command) and two aspects (Perfective and Imperfective). Tense is not marked on the verb in Gbaya (Roulon, 1975; Roulon-Doko, 1994). Verbs always express a process where the obligatory subject is either external to the process (transitive construction = transitive voice) or included in the process (intransitive construction = middle voice).

### 2.1 Tonal tokens

Tonal tokens, or morphotonemes (Meeussen, 1967), are inflectional morphemes that impose tonal patterns or trigger tonal alternations. Three cases of tonal tokens are discussed.

**TAM markers.** The 19 TAM markers are all tonal tokens. They include a verbal pattern that we place in front of the verb root (R) for the sake of regularity, even if they contain suffixal elements. For TAM markers, we follow the UD annotation scheme: they receive **upos=AUX** and depend on the root by a **aux** relation: see sentences (1) and (2).<fnref n="3" />

<footnote n="3">³In fact, TAM marker are distributional heads, because they control the distribution of the verb forms, which is different between finite and non-finite forms. In consequence, auxiliaries are generally treated as heads in SUD. Due to the particular status of Gbaya’s TAM markers, which are only inflectional morphemes, we have treated them as dependents, following UD.</footnote>
(1) Wàntò kúr
H-kur
NPR IPFV-get_up
'Wanto gets up.'

<figure><img src="image_3.png" /></figure>

(2) mè hér
mé-B H-hér-VV
2SG-INJ INJ_IPFV-wrap-DUR
'Wrap it.'

<figure><img src="image_4.png" /></figure>

(3) ʔá kàyá gbàŋá sùnù
BHa-kai-H gbàŋá-H
3SG PFV-gather-MT hard_part-MT sesame
'He collects sesame seeds.'

<figure><img src="image_5.png" /></figure>

(4) dáà kɔ́ bêm
father of child
'The child's father.'

<figure><img src="image_6.png" /></figure>

In (1), we show the realis imperfective (IPFV), which is realized by a high tone H-. In (2), we show the injunctive-imperfective (INJ_IPFV), which is also realized by a high tone H- on the verb, but also imposes a low tone -B on its subject, which must obligatorily be a personal pronoun. Such a construction forces us to make choices when converting the treebank to the word-based UD annotation scheme. The fusion of the personal pronoun and the low tone could be analyzed an alternative form of the pronominal subject (our choice) or with an auxiliary bearing a pronominal index. If the second case is common in many languages, it would have been uncommon in Gbaya, which has no other cases of pronominal indices and where clauses always have an overt subject.

**The floating tone -H.** There are regular tonal modifications linked to the presence of a floating high tone -H, which occurs between two words. It modifies the tonal pattern of the first word depending on the first tone of the second word according to fixed rules, except in the case of a high pattern. This floating high tone can mark grammatical distinctions (functioning as a supra-segmental marker, TM in the glosses). It occurs in two

con texts. Either (i) it is structurally attached to certain words (preposition, perfective verbal marker, etc.), involving no choice on the part of the speaker, similar to class markers, for instance (as the first -H in (3)); or (ii) it functions as a connective linking the two nouns of a genitive phrase (second -H in (3)) contrasting with the genitival SN with segmental connective kɔ́ (4).

In the first case, it is analyzed as an affixe of first word, with **upos=X** and linked to the root by a relation **aff** (it represents 75% of the occurrences in the treebank). In the second case, it is analyzed with **upos=ADP**, like the real **ADP kɔ́**. In SUD, **ADPs** are analyzed as the head of the adpositional phrase and the noun depends on the **ADP** by a relation **comp**.

**Multicategory markers.** Multicategory markers are suffixes or morphotonemes that can combine with lexemes of different parts of speech. We treat all of them as suffixes and give them **upos=DET**. They are the anaphoric -í, the locative -ɛ̃, the insistent -V polar tone, the durative -VV, the suffix -à (definite, nominalizer). They are not exclusive from each other. See (5) and (6).
(5) dɔŋzáìí
dɔŋ-H-á-íí
behind-MT-NMLS-ANAPH
'After that'

<figure><img src="image_7.png" /></figure>

(6) ʔà gáíí
ʔà H-gai-VV
3SG IPFV-bail-DUR
'She bails (the water) for a long time'

<figure><img src="image_8.png" /></figure>

(7) ʔám té-fè
ʔám té-B-fe
1SG VIRT-IPFV-die
'I'm going to die.'

<figure><img src="image_9.png" /></figure>

(8) jínám
jîm-H-ám
name-MT-1SG
'My name'

<figure><img src="image_10.png" /></figure>

(9) bám
H-ba-ám
INJ_IPFV-catch-1SG
'Catch me'

<figure><img src="image_11.png" /></figure>

## 2.2 Clitics

Personal pronouns have a free form when they are used as a subject and placed before the verb (cf. ʔám in (7)). When they are placed after any term, they cliticized on it and loose the initial consonant when it is the glottal /ʔ/ (cf. =ám in (8) and (9)).

All personal pronouns are treated in this way, even those that begin with a different consonant and have the same form in all positions (2SG mé vs =mé, 3PL wà vs =wà)

## 3 Sentence segmentation

Every verb has an overt subject, except in two constructions, relative clauses and coordination of clauses: two successive clauses that share the same subject can be coordinated without repeating the subject before the verb in the second clause. See for example sentence (10).

This gives us a very simple criteria to segment our spoken corpus into sentences: a sentence contains one and only one non-subordinated verb with a subject. A coordinated clause with the main clause will be attached the same sentence if and only if the verb has no subject. This follows the prescriptions of previous spoken corpora (Kahane et al., 2021).

Additionally, there's a case of close coordination without an explicit marker: when two clauses share the same subject, the subject is omitted in the second clause. This subject omission, which goes against the norm of repeating the subject, is annotated with conj:coord, linking the second verb (without subject) to the first.
(10) wà dè nè sáàkà kɔ́à ?èá hɔ́gɔ́ɔ́ɔ́ yɔ́ nè mò
3PL IPFV-do CIRC celebration of-3SG only for_a_long_time IPFV-dance CIRC thing
kádi wholly

‘They just celebrate her for a long time and they dance until they’re exhausted.’

<figure><img src="image_12.png" /></figure>

(11) ?àm kpáwà
?B-àm and.so-1SG IPFV-find-3PL
‘And so I met them’

<figure><img src="image_13.png" /></figure>

(12) ?èè ká fùù yák ná
coord coord
then andThen flour IPFV-leave NEG
‘Then the flour didn’t leave again’

<figure><img src="image_14.png" /></figure>

# 4 Some syntactic constructions

We give an overview of several syntactic constructions, some of them unusual in the current UD collection, such as the reported speech construction.

## 4.1 Sentence coordinating conjunction

Clauses are usually coordinated, expressing the speaker’s enunciative choice. There are eight coordinating conjunctions (plus four variants), such as ?á-nè ‘and now’, ká ‘and then’ or B- ‘and so’ a low tone on the subject personal pronoun (11). The coordinating conjunction ?èè ‘then’ can combine with all the others coordinating conjunctions (12).

## 4.2 Sentence particles

In addition to the coordinating conjunctions, Gbaya has a system of nine enunciative particles, which are always placed at the end of a clause and serve an enunciative function by specifying the speakers point of view. We categorize them

as PART and introduce the relation discourse:sp (sp for sentence particle), already used for Chinese treebanks (Leung et al., 2016).

The sentence particles must be distinguished from the discourse markers, which are analyzed as interjections (INTJ) and receive the function discourse (without an extension).

## 4.3 Adverbial clauses

In SUD, subordinating conjunctions are analyzed as the head of the clause, with the verb as a comp (13).

In Gbaya, however, many subordinate clause relationships are not marked by a subordinating element; rather, it is the verb form itself that marks the subordination. These are the TAM-bound forms. We provide the example of the hypothetical, which renders the clause dependent on a main
(13) *kàà* pí ?éráà kò gúé ká gúé ká gúé ?á hɛ́ɛ́-hɛ́ when-3SG IPFV-put hand-MT-3SG in fish_hole andThen fish_hole andThen fish_hole BE-LOC just_here ‘When she puts her hand in the fish hole, it’s a fish hole all right.’

<figure><img src="image_15.png" /></figure>

clause that must follow (see example (14) where
the subordinative clause is in blue).

4.4 Relative clauses

There is no relative pronoun in Gbaya, but only
one pure relativizer *nè*, which is analyzed as a sub-
ordinating conjunction. In 11 of the 18 examples
of our treebank, the subject is extracted and the
clause has a gap in the subject position (see (15)
where the relative clause is in blue and the domain
name in orange).

Object relative clauses have also a gap in the
object position, but in locative relative clause there
is an adverb in the extracted position. Gbaya has
also an original construction with a nominalized
verb as the antecedent, which must be repeated in
the relative clause (16).

4.5 Serial verb construction

Serial verb constructions consists of the expansion
of a verb in predicative position by another verb
in the infinitive (perfective, imperfective, or vir-
tual), within the limit of a sequence of three verbs
V1.TAM V2.INF [V3.INF]. In the treebank, V1
functions as the root, V2 is linked to V1 by a
compound: svc relation (17).

4.6 The reported speech

Reported speech constitutes an original construc-
tion in Gbaya, combining two clauses and two
enunciations. These two clauses are interde-
pendent neither subordinated, as in subordina-
tive clauses, nor sequential, as in coordinated
clauses. The first clause, referred to as the “quot-
ing speech”, introduces the speaker; the second,
the “quoted speech’, provides the content of the
discourse. Without going into the specifics of this
construction, it is important to note that the quoted
speech alone is sufficient to establish reported dis-
course. The quoting speech is rarely verbal and

is often limited to the speakers name (eventually
followed by a particle, the most common being
*ndé*). The quoted speech may begin with a men-
tion of the addressee, which can be followed by the
particle *nà*. Note that *ndé* have the primary role
of being a sentence particle expressing interroga-
tion, and *nà* have the primary role of being a verb
modifier expressing negation. We analyze both
the speaker and the addressee with a new relation
which we call **discourse: participant**. See (18)
and (19).

4.7 Topicalization

In Gbaya, topicalization brings a noun or noun
phrase (the topic) to the front of the sentence,
followed without pause by the comment. When
the subject occupies this initial position, specific
markers (a resumptive pronoun, a topicalization
particle, or both) are required to indicate its topi-
cal status. Moving a direct object or oblique com-
plement to the front of the sentence is enough to
topicalize it, sometimes reinforced by a topicaliza-
tion marker. If the object is animate, a resump-
tive pronoun follows the verb; if it is inanimate,
the position remains empty. Another construction
topicalizes the verb by placing a verbal noun first,
followed immediately by the same verb.

4.8 Focalization

In Gbaya, noun focalization is marked by the iden-
tifiers nɛ́ or mɛ̌-nɛ́ / mɔ̌-nɛ́. The sentence begins
with this identifier, followed by a clause in which
the focused element functions as subject, object,
or circumstantial complement. Such a construc-
tion exhibits a cleft extraction that splits the verbal
predication into two parts. Only nɛ́ combines with
the potential verb form to express negation, unlike
mɛ̌-nɛ́, which occurs only in affirmative clauses.
Verbal focus uses nɛ́, functioning like an applica-
tive suffix placed after the conjugated verb, target-
(14) Wàntò mɛ́ né-sìá mè káí bɛ́ fùù
NPR 2SG HYPO-PFV-return 2SG-INJ INJ_IPFV-collect little flour

'Wanto if you return, take some flour.'

<figure><img src="image_16.png" /></figure>

(15) ká nɔ́ yɛ́rè nè gbèè bókápáà pɛ́m ess ná
and_then fat buffalo REL PFV-kill-MT sister-MT-3SG IPFV-suit yet NEG

'The way buffalo fat dulled his sisters senses is just unbelievable.'

<figure><img src="image_17.png" /></figure>

(16) kóàà nè ?éí kòò bêm mbè zɔ́k mò ná ká
NV-give_birth REL LOGSG PFV-give_birth-MT child amazing IPFV-see thing DISC and_then
bêmí ?á-nè dèè dɛ́p-kéyɛ́p ?òóyè
child-ANAPH TOP PFV-dMT tall_(6_8 Years_old) ofóbcourse

'Having surprisingly given birth to a child, she realizes that the child is of course grown up [6-8 years].'

<figure><img src="image_18.png" /></figure>
(17) ?éí nèè V1 kpéé V2 yì
LOGSG PFV-go-MT INF_IPFV-close river
'I've gone to block the river (scoop fishing).'

<figure><img src="image_19.png" /></figure>

(18) ?á-nè wà wàntò mé té-?ò
and_now they Wanto you lying_down
dîì
where

‘and now they (say): Wanto, where do you want to sleep?’

<figure><img src="image_20.png" /></figure>

ing the immediately following element: the ob-
ject (with transitive verbs), a circumstantial com-
plement (with intransitives), or, if no complement
follows, a verbal noun derived from the same verb.

5 UD version of the treebank

Like for the mSUD annotation, the UD version of
the Gbaya treebank is produced in two steps. First,
the word tokenisation is modified to match the syn-
tactic word level expected by UD. Then the regular
conversion for SUD to UD (Gerdes et al., 2018b)
is used to produce the UD version.

**5.1 Word-level tokenisation**

Word-level tokenisation is obtained from the original annotation by merging inflectional morphemes with the tokens to which they are attached.

There are few cases where the inflectional mor-
pheme is not directly syntactically related to its
neighbour token. In the example below, the suf-
fix -B is not syntactically linked to the previous
token ?éné. We have built a dedicated heuristic to
compute the necessary syntactic structure after the
fusion: in the example, we want to keep the subj

relation in the final structure.

<figure><img src="image_21.png" /></figure>

After affixes merging, the example above is con-
verted into:

<figure><img src="image_22.png" /></figure>

Note that in the word-based version, the
morpheme-based analysis is indicated in the MSeg
and MGloss features.

5.2 Conversion to UD

The annotation obtained in the previous step is not
a regular SUD format. Nevertheless, the univer-
sal conversion from SUD to UD can be applied
because the Gbaya word-level format is between
SUD and UD: adpositions are heads, as in SUD,
and auxiliaries are dependent, as in UD. Thus,
only a subset of the conversion rules is activated
during the conversion process. With sentence (19)
the 3 annotation formats are given: first the an-
notated format at morpheme level, then the SUD
annotation at word level and then UD annotation
(also at word level).

6 Conclusion

The Gbaya treebank is the first treebank of a new
genus within the Niger-Congo family, and only the
Fourteenth treebank (along with Tswana, Yoruba
and Wolof) of the greater Niger-Congo family,
which comprises over 1,500 languages, including
the 400 Bantu languages. Gbaya differs from
Bantu languages in the absence of nominal classes
and agreement rules. It has a highly developed
tonal inflection system, but virtually no affixes.
We have chosen to develop a morpheme-based
treebank in order to highlight the elegance of this
language's grammatical system and to have a re-
source that combines the interlinear glosses pre-
viously developed by Paulette Roulon-Doko with
(19) *dáà ké bêm ná ?éí nèè* | *kpéé yì*
father of child DISC LOGSG PFV-go-MT INF_PFV-close river

'[She says] To the child's father I go to block the river.'

<figure><img src="image_23.png" /></figure>

syntactic analysis. The treebank is also distributed
in a word-based UD version, where morphologi-
cal information remains accessible in the MSeg and
MGloss features.

Acknowledgements

We would like to thank the three reviewers for their
constructive feedback on the paper. This work has
been supported by the French National Research
Project Autogramm (ANR-21-CE38-0017).

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