Word sense disambiguation means choosing between two meanings of the same word (we assume we already know the part of speech). This can be important in machine translation between less-closely related languages. The problem was elucidated most famously by Yehoshua Bar-Hillel, who asks us to consider the following sentence:
- Little John was looking for his toy box. Finally he found it. The box was in the pen.
The word pen may have two meanings:
- Something you use to write with
- A container of some kind
To a human, the meaning is obvious, but Bar-Hillel claimed that without a "universal encyclopaedia" a machine would never be able to deal with this problem. Figuring out which sense to use when a word is ambiguous is called word sense disambiguation, and is a big research area.
However, importantly, many of the possible meanings and nuances identified by lexicographers do not affect machine translation. E.g. the English term hospital can refer to both an organisation and a concrete building, but regardless of which meaning is used in a sentence, in Norwegian it still becomes sjukehus. Thus we use the term lexical selection when we speak of those word senses that matter to MT. More on this in the article Lexical selection.
 Further reading
- Ide, N. and Véronis, J. (1998) "Word Sense Disambiguation: The State of the Art". Computational Linguistics 24(1)
- Agirre, E. and Edmonds, P., editors (2007). "Word Sense Disambiguation: Algorithms and Applications". Volume 33 of Text, Speech and Language Technology
- Navigli, R. (2009) Word Sense Disambiguation: A Survey. ACM Comput. Surv. 41, 2, Article 10