Parsing Free Word Order Languages in the Paninian Framework

Parsing Free Word Order Languages in the Paninian Framework Akshar Bharati Rajeev Sangal Department of Computer Science and Engineering Indian Institute of Technology Kanpur Kanpur 208016 India Internet: sangal@iitk.ernet.in Abstract There is a need to develop a suitable computational grammar formalism for free word order languages for two reasons: First, a suitably designed formal- ism is likely to be more efficient. Second, such a formalism is also likely to be linguistically more ele- gant and satisfying. In this paper, we describe such a formalism, called the Paninian framework, that has been successfully applied to Indian languages. This paper shows that the Paninian framework applied to modern Indian languages gives an elegant account of the relation between surface form (vib- hakti) and semantic (karaka) roles. The mapping is elegant and compact. The same basic account also explains active-passives and complex sentences. This suggests that the solution is not just adhoc but has a deeper underlying unity. A constraint based parser is described for the framework. The constraints problem reduces to bi- partite graph matching problem because of the na- ture of constraints. Efficient solutions are known for these problems. It is interesting to observe that such a parser (de- signed for free word order languages) compares well in asymptotic time complexity with the parser for context free grammars (CFGs) which are basically designed for positional languages. 1 Introduction A majority of human languages including Indian and other languages have relatively free word or- der. tn free word order languages, order of words contains only secondary information such as em- phasis etc. Primary information relating to 'gross' meaning (e.g., one that includes semantic relation- ships) is contained elsewhere. Most existing compu- tational grammars are based on context free gram- mars which are basically positional grammars. It is important to develop a suitable computational grammar formalism for free word order languages for two reasons: 1. A suitably designed formalism will be more ef- ficient because it will be able to make use of primary sources of information directly. 2. Such a formalism is also likely to be linguisti- cally more elegant and satisfying. Since it will be able to relate to primary sources of informa- tion, the grammar is likely to be more econom- ical and easier to write. In this paper, we describe such a formalism, called the Paninian framework, that has been successfully applied to Indian languages. 1 It uses the notion of karaka relations between verbs and nouns in a sentence. The notion of karaka relations is cen- tral to the Paninian model. The karaka relations are syntactico-semantic (or semantico-syntactic) re- lations between the verbals and other related con- stituents in a sentence. They by themselves do not give the semantics. Instead they specify re- lations which mediate between vibhakti of nom- inals and verb forms on one hand and semantic relations on the other (Kiparsky, 1982) (Cardona (1976), (1988)). See Fig. 1. Two of the impor- tant karakas are karta karaka and karma karaka. Frequently, the karta karaka maps …

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