One Sense per Collocation and Genre/Topic Variations

One Sense per Collocation and Genre/Topic Variations David Martinez IXA NLP Group University of the Basque Country 649 pk. 20.080 Donostia. Spain jibmaird@si.ehu.es Eneko Agirre IXA NLP Group University of the Basque Country 649 pk. 20.080 Donostia. Spain eneko@si.ehu.es Abstract This paper revisits the one sense per collocation hypothesis using fine-grained sense distinctions and two different corpora. We show that the hypothesis is weaker for fine-grained sense distinctions (70% vs. 99% reported earlier on 2-way ambiguities). We also show that one sense per collocation does hold across corpora, but that collocations vary from one corpus to the other, following genre and topic variations. This explains the low results when performing word sense disambiguation across corpora. In fact, we demonstrate that when two independent corpora share a related genre/topic, the word sense disambiguation results would be better. Future work on word sense disambiguation will have to take into account genre and topic as important parameters on their models. Introduction In the early nineties two famous papers claimed that the behavior of word senses in texts adhered to two principles: one sense per discourse (Gale et al., 1992) and one sense per collocation (Yarowsky, 1993). These hypotheses were shown to hold for some particular corpora (totaling 380 Mwords) on words with 2-way ambiguity. The word sense distinctions came from different sources (translations into French, homophones, homographs, pseudo-words, etc.), but no dictionary or lexical resource was linked to them. In the case of the one sense per collocation paper, several corpora were used, but nothing is said on whether the collocations hold across corpora. Since the papers were published, word sense disambiguation has moved to deal with fine- grained sense distinctions from widely recognized semantic lexical resources; ontologies like Sensus, Cyc, EDR, WordNet, EuroWordNet, etc. or machine-readable dictionaries like OALDC, Webster's, LDOCE, etc. This is due, in part, to the availability of public hand-tagged material, e.g. SemCor (Miller et al., 1993) and the DSO collection (Ng & Lee, 1996). We think that the old hypotheses should be tested under the conditions of this newly available data. This paper focuses on the DSO collection, which was tagged with WordNet senses (Miller et al. 1990) and comprises sentences extracted from two different corpora: the balanced Brown Corpus and the Wall Street Journal corpus. Krovetz (1998) has shown that the one sense per discourse hypothesis does not hold for fine- grained senses in SemCor and DSO. His results have been confirmed in our own experiments. We will therefore concentrate on the one sense per collocation hypothesis, considering these two questions: • Does the collocation hypothesis hold across corpora, that is, across genre and topic variations (compared to a single corpus, probably with little genre and topic variations)? • Does the collocation hypothesis hold for free- grained sense distinctions (compared to homograph level granularity)? The experimental tools to test the hypothesis will be decision lists based on various kinds of collocational information. We will compare the performance across several corpora (the Brown Corpus and Wall Street Journal …

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