Extending the usage of adjectives in the Z ulu A f WN (2023)

Abstract: The African languages Wordnet (AfWN) for Zulu (ZWN) was built using the expand approach, which relies on the translation of concepts in the Princeton WordNet (PWN), while retaining their PWN lexical categories. In this paper the focus is on the adjective as PWN lexical category. What is considered adjectival information (provided both attributively and predicatively) in English, is usually verbalised quite differently in Zulu - often as verb or copulative constructions - as may be seen by inspecting the Zulu written forms in “adjective” entries in ZWN. These written forms are not complete Zulu verb or copulative constructions and in order for them to be useful, tense, polarity and agreement have to be added. This paper presents a grammar-based approach to recover important morphosyntactic information implicit in the ZWN “adjective” written forms in order to derive a tool that would assist a user of the ZWN to render and analyse correct full forms automatically as desired by the context in which an “adjective” is used.

## introduction the central role that the pwn has come to play in computational lexical semantics and meaning representation is well known and has given rise to the development of wordnets for many languages, including the african languages, with the expectation that they would play a similar role in the natural language processing (nlp) of these languages. from the outset, the developers of afwn were confronted with, amongst others, the structural discrepancies that arise in creating "adjective" entries @xcite . this resulted in "adjective" entries that are mostly based on word categories other than zulu adjectives -categories that exhibit their own complex morphosyntactic structure. for this reason, these entries pose unique challenges for the potential users of the afwn, creating the need for computational tools and methods for using them. we are not aware of any language other than those of the afwn that exhibit this characteristic and has a wordnet. indeed, dealing with this issue has not been discussed elsewhere except for northern sotho in @xcite . in this paper we propose a novel approach for extending the usage of "adjective" entries in the zwn and we provide a tool that could in due course support applications of the zwn. ## background it is often stated that the expand model, by "which the source wordnet, usually the english pwn, is translated into the target language, relies on the assumption that the new language shares an underlying structure with the pwn" @xcite . it is also widely stated that this model is often used in cases where the target language is under-resourced. the afwn developers adopted the expand model, mainly on the basis of the underresourcedness of the african languages. what has received less attention is the extent to which the african languages "share an underlying structure with the pwn". the pwn has four main lexical categories: nouns, verbs, adjectives and adverbs. in this article we focus on what is known as the "adjective" (as noun qualifier) in the pwn and how noun qualification in zulu presents unique challenges for "adjective" entries in the zwn. english adjectives (pwn) seldom map to adjectives in zulu. zulu employs qualificatives to modify nouns, namely the adjective, the descriptive possessive, the verbal relative, copulative relative and the enumerative foot_0 @xcite . the question arises how the zwn should apply the expand model in this situation. @xcite notes that for northern sotho, "[t]he challenge ... is that while they are all meaning equivalents of the same english word category, they straddle a number of morphosyntactic categories in northern sotho, which nevertheless share a semantic function." this also applies to zulu in that the written forms of the "adjective" entries in the zwn represent a diverse set of complex mophosyntactic constructions. our aim in this paper is to use a computational grammar to recover these implicit constructions of the zwn written forms and to use this information to generate and analyse all full forms for varying tense, polarity and agreement. we describe how this generation and analysis can be exposed via an end-user command line tool. 2 the structure of the paper is as follows; in section 3 we briefly discuss the afwn, noting aspects of the zwn that are applicable to our work. in section 4 we focus on noun qualification and the "adjective" as lexical entry. more specifically, we discuss the challenges and limitations surrounding the choice of written forms to represent complex morphosyntactic constructions in zulu. section 5 introduces the gf zulu resource grammar (zrg): we explain how the verb phrase is modelled and how it facilitates the rendering of specific full forms of verb phrases. the extension procedure using the zrg in section 6 sets out the main contribution. section 7 presents an evaluation as well as a discussion of the results. ## the afwn development of the afwn started in 2008 by following the expand approach -considered the preferred approach (as opposed to the merge approach) for under-resourced languages, using the cbc. 3 over time the need to be more african focused was recognised, which led to the use of the sil-cawl, foot_3 consisting of 1700 terms which resulted from linguistic research in africa. although the pwn includes four open lexical categories (noun, verb, adjective and adverb), the publications of the afwn, more specifically the zwn, have up to now addressed predominantly nouns and verbs (see, for example, @xcite ). these two lexical categories are known to allow for a mostly well-behaved mapping between the nouns and verbs of english and zulu, provided that the concepts are lexicalised in both languages. the lexical category of adjective, however, does not allow for an equally well-behaved mapping. this has important consequences for the structure and subsequent use of zwn entries that are labelled as "adjective", as will be explicated in subsequent sections. ## the gf zulu resource grammar grammatical framework is a computational grammar framework and programming language for writing multilingual grammars. a gf multilingual grammar has an abstract syntax as interlingua and one or more concrete syntaxes, one for each language. the abstract syntax defines categories and functions which are implemented in the concrete syntaxes as linearisation categories and linearisation functions. by defining the linearisation categories and functions of a language, the gf runtime is enabled to linearise abstract syntax trees into natural language strings or to parse natural language strings into abstract syntax trees @xcite . a central project of grammatical framework has been the development of a resource grammar library (rgl), the core of which is a common abstract syntax that defines linguistic structures found in most languages. for example, it includes categories for nouns and verbs and functions for predication and noun modification. the original intent of the rgl was to serve as a linguistic software library to enable rapid development of application specific grammars @xcite . implementing the rgl categories and functions for a language would once and for all capture the general morphology and syntax of the language, to be reused by grammars aimed at a specific use case or application. more recently, however, attempts have been made to employ the general use grammars of the rgl towards wide-coverage parsing @xcite . the rgl supports close to 40 languages and has, for example, been used to develop a parallel swedish and bulgarian wordnet resource @xcite . the zulu resource grammar (zrg) models the morphology and syntax of zulu. this is achieved by the implementation of a deliberate selection of functions from the common abstract syntax, in addition to a set of extra language specific abstract functions. 9 a large lexicon and an extension that defines chunks have been developed to enable the use of the zrg as a wide-coverage zulu parser. in the gf rgl, as in the zrg, the vp category is used to model generalised predicates for which tense, polarity and agreement is not yet fixed. vps are used in two main ways, namely to supply the predicate in main clauses and to construct relative in the zrg, the vp linearisation category contains a table with all full forms of the predicate as it appears in the main clause and the relative clause, for every tense, polarity and agreement value, and also, if applicable, distinguishing between a long and a short form. figure 1 shows a snippet of the code defining the vp linearisation category, along with the parameters that define the dimensions of this table. for example, in the vp for the verb bon_v ('to see'), we can obtain the indicative, present, positive by selecting the values maincl, third c1_2 sg, pos, prestense and true, which will yield the form uyabona ('sees'). implementing a function that takes a vp as argument therefore involves making the appropriate selections based on the context in which the vp is used. ## extending the usage of zwn adjectives the zwn is under active development and a second release is expected soon. for this publication, our work was based on preliminary data acquired from the developers ahead of the new release. due to the status of development at the time, the data dump did not include links to the senses of pwn 3.1 or the zulu usage examples. however, inspection of the data showed that a significant number of adjective entries had remained essentially in tact from the first version (1338 out of 1590). we therefore decided to focus on the adjective entries in the preliminary data of the new release that also appeared in the first release. in this way, we could ensure that the zwn written forms in our dataset were as current as possible, while their english senses could be obtained via the first release's links to pwn 2.0. our contribution is three-fold: we recover implicit morphosyntactic constructions from the written forms by parsing them using the zrg; we provide functionality to generate and analyse full forms of these constructions; we do this via a mostly automatic process, which can be reused for future versions of the zwn, and for the other languages in the afwn once resource grammars for these languages are available. the notion of using a fully fledged syntax parser for parsing mostly single token written forms of a wordnet seems incongruous at first glance. however, as an agglutinating language with a conjunc-use tense pol. zulu english pred. pres. ## evaluation and discussion as noted in section 6.2, when considering those written forms for which a morphological analysis could be found for each token, a plausible parse for 87.9% of written forms could be obtained. this was used the basis for an application grammar and wrapper tool that could generate and analyse full forms of adjectives with different tense, polarity and agreement values, as well as form, whether attributive or predicative. this is a novel contribution. the zulu resource grammar along with the gf runtime system is the foundation of this generation and analysis capability. while some work has been done to develop gf resource grammars for other african languages @xcite , these grammars have not yet been demonstrated to support the kind of application grammar development pre-sented here. as such, there is no baseline to compare our work to, which presents a challenge for evaluation. the only comparable computational tool, in terms of accuracy and scope, is the zulmorph morphological analyser, which is an fst that can be applied to surface forms in order to obtain full morphological analyses and vice versa. while it cannot disambiguate analyses for multitoken expressions and hence is not suitable for the generation and analysis task presented here, it can be utilised in the evaluation of the output of the zulu resource grammar, as mediated by the adjective application grammar. ## conclusion the analysis in the previous section illustrates the morphosyntactic diversity of the adjective-like zulu qualificatives. we have shown how a computational grammar-based approach can overcome the challenge this poses in order to take full advantage of the zwn by facilitating its potential use in nlp applications for zulu. the process we have developed could be repeated whenever new versions of the zwn are released. moreover, as shown in the previous section, the adjective-like qualificatives in the zwn typically represent constructions based on verbs and nouns. future work will include developing functionality to similarly generate and analyse full forms of verb and noun entries of the zwn, as well as replicating the work for other languages in the afwn once resource grammars for them are developed.