Understanding Verbs Based on Overlapping Verbs Senses
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Understanding Verbs based on Overlapping Verbs Senses Kavitha Rajan Language Technologies Research Centre International Institute of Information Technology Hyderabad (IIIT-H) Gachibowli, Hyderabad. 500 032. AP. India. [email protected] Abstract (Schank and Abelson, 1977) were developed from the CD theory. None of the descendant Natural language can be easily understood by theories of CD could focus on the notion of everyone irrespective of their differences in 'primitives' and the idea faded in the subsequent age or region or qualification. The existence works. of a conceptual base that underlies all natural Identification of meaning primitives is an area languages is an accepted claim as pointed out intensely explored and a vast number of theories by Schank in his Conceptual Dependency have been put forward, namely, (PRO: (CD) theory. Inspired by the CD theory and theories in Indian grammatical tradition, we Conceptual semantics (Jackendoff, 1976), propose a new set of meaning primitives in Meaning-text theory (Mel’čuk,1981), Semantic this paper. We claim that this new set of Primes (Wierzbicka, 1996), Conceptual primitives captures the meaning inherent in dependency theory (Schank, 1972) Preference verbs and help in forming an inter-lingual and Semantics (Wilks, 1975) CONTRA: Language of computable ontological classification of Thought (Fodor, 1975)). Through our work, we verbs. We have identified seven primitive put forward a set of seven meaning primitives overlapping verb senses which substantiate and claim that the permutation/combination of our claim. The percentage of coverage of these seven meaning primitives along with these primitives is 100% for all verbs in ontological attributes is sufficient to develop a Sanskrit and Hindi and 3750 verbs in English. computational model for meaning representation across languages. 1 Introduction This paper looks at the Conceptual Dependency Theory created by Roger Schank Communication in natural language is simple. (Schank, 1973; Schank, 1975) and compares it Looking at the ease to learn and communicate in with theories in Indian grammatical tradition. We and across natural languages, the claim of discuss these in section 2 and section 3. We then existence of interlingual conceptual base analyze if we can modify Schank's approach to (Schank, 1972) seems plausible . define a more efficient set of primitives. We Conceptual Dependency (CD) theory tried to conclude by introducing the small set of meaning represent a conceptual base using a small set of primitives which we have found to cover all meaning primitives. To achieve this goal, they verbs in Indian languages like Sanskrit, Hindi put forward a proposal consisting of a small set and almost all verbs in English. of 12 primitive actions, a set of dependencies which connects the primitive actions with each 2 Conceptual Dependency other and with their actors, objects, instruments, According to Schank, linguistic and situational etc. Their claim was that this small set of contexts in which a sentence is uttered is representational elements could be used to important for understanding the meaning of that produce a canonical form for sentences in sentence. The CD theory was developed to create English as well as other natural languages. a theory of human natural language Representational theories like Scripts, Plans, understanding. The initial premise of the theory Goals and Understanding(SPGU) representations 59 Proceedings of the ACL Student Research Workshop, pages 59–66, Sofia, Bulgaria, August 4-9 2013. c 2013 Association for Computational Linguistics is: basis of natural language is conceptual. century BC) put forward the bhāva-based According to the theory, during communication, definition to define all types of verbs. According to-and-fro mapping happens between linguistic to Nirukta verse 1.1 (Sarup, 1920) the structures and the conceptual base through characteristic that defines a verb form is its verb concepts. It is due to the existence of this having bhāva as its principal meaning. In conceptual base and concept based mapping that Sanskrit, bhāva is a morphological form of a person, who is multilingual, is able to switch bhavati and bhavati means 'happening'. So between languages easily. structure of bhāva can be defined as structure of The conceptual base consists of concepts and happening which is explained in section 4.1. the relations between concepts. Therefore, it is According to sage Vārsyāyá ṇi, Nirukta verse responsible for formally representing the 1.2 (Sarup, 1920), there are 6 variants of bhāva concepts underlying an utterance. There are three or verb which, we believe, can be compared to 6 types of concepts: a) nominal; b) action and c) fundamental processes. That is, a process 'verb' modifier. We will concentrate only on 'action' consists of six stages. They are: since our work is related to verbs. coming into being - jāyate CD’s basic premise is that the ACTION is the 'is born, comes into being' basis of any proposition that is not descriptive of existing - asti 'is' a static piece of the world. Conceptualization changing - vipariṇ amate consists of action, actors and cases that are 'undergoes modification' dependent on that action. An ACTOR is defined increasing - vardhate as an animate object and an OBJECT as any 'grows, increases' concrete physical entity. CD representations use diminishing - apaksIyaté 'diminishes' 12 primitive ACTs out of which the meaning of ceasing to be - vinasyatí f'perishes' verbs, abstract and complex nouns are constructed. 4 Our Approach Primitives are elements that can be used in We are trying to use existing theories in the many varied combinations to express the traditional school of Sanskrit language, namely, meaning of what underlies a given word. In CD, Navya-Nyāya for identification and formal primitives were arrived at by noticing structural representation of primitive actions. We work similarities that existed when sentences were put within the formal framework of Neo- Vaisesiká into an actor-action-object framework. Using Formal Ontology (NVFO)2. these acts, set of states and set of conceptual roles, it is possible to express a large amount of 4.1 Form of verb the meanings expressible in a natural language. Happening is formally conceived as punctuation 3 Indian grammatical tradition between two discrete states in a context. Since every happening consists of minimally two The Nirukta1(Sarup,1920; Kunjunni et. al., 1990) different states, there is an atomic sense of statement "Verbs have operation as its movement in it. Movement means whenever an predominant element" proposes that “process” is action takes place two states come into existence. the most important element in a verb. As all The initial state, at the beginning of an action and words can be derived from verbal roots, we can a final state, after the completion of the action. say that words in a natural language are either The two states can be same or different. Time is activities (verbs) or derived from some activity an inseparable part of this structure because (nouns). For example: between initial and final states there can be n rājā (king) is derived from (the root) rāj (to number of intermediate states which are shine) sequential. vṛkṣa (tree) is derived from (the root) v ṛ (to Happening (Sanskrit, bhavati) is the change of cover) kṣ ā (the earth) state from one to another in a context. According Verb is called kriyā in Sanskrit. kriyā stands to Bhartṛihari (5th century CE) every verb has for action or activity. Verbs consists of both action and state verbs. Sage Kātyāyana (3rd 2 Vaisesiká́ ontology, due to Kaṇāda (Rensink, 2004), Pras ́astapāda (Hutton, 2010) and Udayana (Kaṇāda, 1986) has 1 Nirukta (Kunjunni et.al., page-88). been formalized by Navjyoti (Tavva and Singh, 2010). 60 'sense of sequence' and 'state' in it. Hence, every identifying frequent verbs is explained using a verb projects a 'sense of happening', making this sample verb 'fall': sense omnipresent in all verbs. Therefore, Definitions of different verb senses of ‘fall’ from bhavati is a 'universal verb'. In the two different sources are given below: nominalization of bhavati, 'bhāva3' has a formal Source 1 (Dictionary.com): structure and has been named 'punct'4. The (to drop or descend under the force of gravity, formal representation of bhāva is shown in as to a lower place through loss or lack of Figure1. support), (to come or drop down suddenly to a The structure of (universal verb) 'punct' is: lower position, especially to leave a standing or < state1 | state2, (Context) Feature Space > erect position suddenly, whether voluntarily or The structure can also be represented in short not), (to become less or lower; become of a format as: < s1 / s2 | FS (C)> lower level, degree, amount, quality, value, number, etc.; decline) Context Source 2 (WordNet): (descend in free fall under the influence of gravity), (decrease in size, extent, or range), State State 1 2 (move downward and lower, but not necessarily all the way), (move in a specified direction), (lose an upright position suddenly), (drop Figure1. Structure of happening oneself to a lower or less erect position) are few From Sanskritist tradition, we have adopted the senses. concept of universal verb. Our original All words in bold represent ‘movement’ in a contribution is that we have defined an negative manner. Since movement is the most ontological structure (see Figure1) to represent common concept, ‘move’ is taken as an ‘universal verb’ and have used it to represent the overlapping primitive verb sense. Other seven primary verb senses (primitives) which we primitives like know, do, is, have, cut, and cover have identified. All verbs in a language can be were obtained by similar procedure. represented formally using this structure. In dictionaries, overlapping verb senses used 4.2 Identifying Overlapping Verbal to explicate meaning of defined verbs, show the senses relatedness of two verbs. The phenomenon known as 'Dictionary circularity' (Wierzbicka, Can we have a few number of primitive meaning 1996) confirms the existence of this claim.