The verbal phrase of Northern Sotho : A morphosyntactic perspective

So far, comprehensive grammar descriptions of Northern Sotho have only been available in the form of prescriptive books aiming at teaching the language. This paper describes parts of the first morpho-syntactic description of Northern Sotho from a computational perspective (Faaß, 2010a). Such a description is necessary for implementing rule based, operational grammars. It is also essential for the annotation of training data to be utilised by statistical parsers. The work that we partially present here may hence provide a resource for computational processing of the language in order to proceed with producing linguistic representations beyond tagging, may it be chunking or parsing. The paper begins with describing significant Northern Sotho verbal morpho-syntactics (section 2). It is shown that the topology of the verb can be depicted as a slot system which may form the basis for computational processing (section 3). Note that the implementation of the described rules (section 4) and also coverage tests are ongoing processes upon that we will report in more detail at a later stage. 1. Language introduction and overview Northern Sotho is one of the eleven national languages of South Africa and one of the four Sotho languages of the South-eastern Language Zone group (S.30 in the classification of Guthrie (1971)): Northern and Southern Sotho, Tswana (“Western Sotho”) and Lozi (Silozi, Rozi). The Sotho languages are written disjunctively (Van Wyk, 1958), i.e. a number of (mostly inflectional) affixes (henceforth “morphemes”) are written separately instead of being merged with the stems that they belong to. Especially Northern Sotho verbs differ significantly from that of other languages, not only in respect to their moods, but also in the many different morpheme constellations that they may appear in. Concerning its computational processing, Northern Sotho language resources and tools have been the subject of a few publications during recent years of which, for space reasons, we can only list a few: a methodology for tagging corpora of Northern Sotho has been designed by Prinsloo and Heid (2005), a number of finite-state tokenizers have been reported upon, concerning its verbs e.g. by Anderson and Kotzé (2006), a first tagset and a tagging experiment have been described by De Schryver and De Pauw (2007). Taljard et al. (2008) defined a more finely granulated tagset of which we partially make use in this paper. Lastly, Faaß et al. (2009) reported on results of tagging Northern Sotho with an approach of disambiguation of polysemous items.1 This paper aims at designing a first morpho-syntactic framework for a number of Northern Sotho verbal constellations.2 The paper does not claim to present a complete description, it is however shown here that a significant fragment of the verbal grammar can be For an overview of NLP resources of the African languages of South Africa, cf. (Roux and Bosch, 2006). This paper focuses on main verbs, it is developed on the grounds of (Faaß, 2010a). depicted with a basic distinction made between elements syntactically subcategorised by the verb stem on the basis of its lexical semantic properties on the one hand, and its inflectional elements on the other. The rules defined here are already in the process of being implemented in a rule-based parser (cf. (Faaß, 2010b) for a first report), however, they may also be used for other purposes, e.g. to produce training data for a statistical parser. Coverage tests are currently in process. 2. Northern Sotho verbs: An Introduction Northern Sotho verbs appear in a variety of moods; for space reasons, we however focus on the independent predicative moods in this paper: indicative, situative and relative (for an overview of the Northern Sotho moods, see e.g. (Lombard, 1985, p. 144)). These moods all appear in the three tenses future, present and past and all may be negated. To mark tense or polarity, each of the moods makes use of specific morphemes to appear in front of the verb stem. Note that except for the missing tense marking, the dependent grammatical moods (consecutive, habitual and subjunctive) basically make use of the same morphemes as described here. The verb stem itself may show specific affixes fused to it, e.g. indicating some of the past constellations (allomorphs of the past tense morpheme -il-), and it appears with certain endings, inter alia -a or -e, that each are predefined by the constellation they must occur in. The ending -a, for example, usually appears in the positive constellations, while some negative ones require -e to appear. Other verbal affixes indicate certain semantic changes (e.g. passive: -w-, applicative voice: -el-, or reciprocal: -an-), of which most change its argument structure, however, these are not relevant for mood detection and thus not furtherly described here. The indicative mood differs from the situative mood insofar as it forms a matrix sentence, cf. (1-a), while the situative Proceedings of the Second Workshop on African Language Technology