Mapping Multilingual Hierarchies Using Relaxation Labeling

Mapping Multilingual Hierarchies Using Relaxation Labeling J. Daud6, L. Padr6 &: G. Rigau TALP Research Center Departament de Llenguatges i Sistemes Inform£tics Universitat Politbcnica de Catalunya. Barcelona (daude, padro, g. rigau}©lsi, upc. es Abstract This paper explores the automatic construction of a multilingual Lexical Knowledge Base from pre-existing lexical resources. We present a new and robust approach for linking already existing lexical/semantic hierarchies. We used a con- straint satisfaction algorithm (relaxation label- ing) to select -among all the candidate trans- lations proposed by a bilingual dictionary- the right English WordNet synset for each sense in a taxonomy automatically derived from a Span- ish monolingua] dictionary. Although on aver- age, there are 15 possible WordNet connections for each sense in the taxonomy, the method achieves an accuracy over 80~. Finally, we also propose several ways in which this technique could be applied to enrich and improve exist- ing lexical databases. 1 Introduction There is an increasing need of having available general, accurate and broad coverage multilin- gual lexical/semantic resources for developing NL applications. Thus, a very active field in- side NL during the last years has been the fast development of generictanguage resources. Several attempts have been performed to pro- duce multilingual ontologies. In (Ageno et al., 1994), a Spanish/English bilingual dictionary is used to (semi)automatically link Spanish and English taxonomies extracted from DGILE (A1- var, 1987) and LDOCE (Procter, 1987). Sim- ilarly, a simple automatic approach for link- ing Spanish taxonomies extracted from DGILE to WordNet (Miller et al., 1991) synsets is proposed in (Rigau et al., 1995). The work reported in (Knight and Luk, 1994) focuses on the construction of Sensus, a large knowl- edge base for supporting the Pangloss machine translation system. In (Okumura and Hovy, 1994) (semi)automatic methods for associating a Japanese lexicon to an English ontology us- ing a bilingual dictionary are described. Sev- eral experiments aligning EDR and WordNet on- tologies are described in (Utiyama and Hasida, 1997). Several lexical resources and techniques are combined in (Atserias et al., 1997) to map Spanish words from a bilingual dictionary to WordNet, and in (Farreres et al., 1998) the use of the taxonomic structure derived from a monolingual MaD is proposed as an aid to this mapping process. This paper presents a novel approach for merging already existing hierarchies. The method has been applied to attach substan- tial fragments of the Spanish taxonomy derived from DGILE (Rigau et al., 1998) to the English WordNet using a bilingual dictionary for con- necting both hierarchies. This paper is organized as follows: In section 2 we describe the used technique (the relaxation labeling algorithm) and its application to hier- archy mapping. In section 3 we describe the constraints used in the relaxation process, and finally, after presenting some experiments and preliminary results, we offer some conclusions and outline further lines of research. 2 Application of Relaxation Labeling to NLP Relaxation labeling (RL) is a generic name for a family of iterative algorithms which perform function optimization, based on local informa- …

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