A Computational Framework for Composition in Multiple Linguistic Domains

A Computational Framework for Composition in Multiple Linguistic Domains Elvan GS~men Computer Engineering Department Middle East Technical University 06531, Ankara, Turkey elvan@lcsl.metu.edu.tr Abstract We describe a computational framework for a grammar architecture in which dif- ferent linguistic domains such as morphol- ogy, syntax, and semantics are treated not as separate components but compositional domains. The framework is based on Combinatory Categorial Grammars and it uses the morpheme as the basic building block of the categorial lexicon. 1 Introduction In this paper, we address the problem of mod- elling interactions between different levels of lan- guage analysis. In agglutinative languages, affixes are attached to stems to form a word that may cor- respond to an entire phrase in a language like En- glish. For instance, in Turkish, word formation is based on suffixation of derivational and inflectional morphemes. Phrases may be formed in a similar way (1). (1) Yoksul-la~-t~r-zl-makta-lar poor-V-CAUS-PASS-ADV-PERS '(They) are being made poor (impoverished)'. In Turkish, there is a significant amount of in- teraction between morphology and syntax. For in- stance, causative suffixes change the valence of the verb, mad the reciprocal suffix subcategorize the verb for a noun phrase marked with the comitative case. Moreover, the head that a bound morpheme modi- fies may be not its stem but a compound head cross- ing over the word boundaries, e.g., (2) iyi oku-mu~ ~ocuk well read-REL child 'well-educated child' In (2), the relative suffix -mu~ (in past form of subject participle) modifies [iyi oku] to give the scope [[[iyi oku]mu~] 9ocuk]. If syntactic composi- tion is performed after morphological composition, we would get compositions such as [iyi [okumu~ 6ocuk]] or [[iyi okurnu~] ~ocuk] which yield ill-formed semantics for this utterance. As pointed out by Oehrle (1988), there is no rea- son to assume a layered grammatical architecture which has linguistic division of labor into compo- nents acting on one domain at a time. As a computa- tional framework, rather than treating morphology, syntax and semantics in a cascaded manner, we pro- pose an integrated model to capture the high level of interaction between the three domains. The model, which is based on Combinatory Categorial Gram- mars (CCG) (Ades and Steedman, 1982; Steedman, 1985), uses the morpheme as the building block of composition at all three linguistic domains. 2 Morpheme-based Compositions When the morpheme is given the same status as the lexeme in terms of its lexical, syntactic, and semantic contribution, the distinction between the process models of morphotactics and syntax disap- pears. Consider the example in (3). (3) uzun kol-lu g5mlek long sleeve-ADJ shirt Two different compositions 1 in CCG formalism are given in Figure 1. Both interpretations are plau- sible, with (la) being the most likely in the absence of a long pause after the first adjective. To account for both cases, the suffix -lu must be allowed to mod- ify the head it is attached to (e.g., lb in Figure 1), or a compound head encompassing the word bound- aries (e.g., 1:~ in Figure 1). 3 Multi-domain …

Content truncated to 500 words