Word sense disambiguation (WSD) is the ability to identify the meaning of words in context in a computational manner. WSD is considered an AI-complete problem, that is, a task whose solution is at least as hard as the most difficult problems in artificial intelligence. We introduce the reader to the motivations for solving the ambiguity of words and provide a description of the task. We overview supervised, unsupervised, and knowledge-based approaches. The assessment of WSD systems is discussed in the context of the Senseval/Semeval campaigns, aiming at the objective evaluation of systems participating in several different disambiguation tasks. Finally, applications, open problems, and future directions are discussed.

Since the inception of the SENSEVAL series there has been a great deal of debate in the word sense disambiguation (WSD) community on what the right sense distinctions are for evaluation, with the consensus of opinion being that the distinctions should be relevant to the intended application. A solution to the above issue is lexical substitution, i.e. the replacement of a target word in context with a suitable alternative substitute. In this paper, we describe the English lexical substitution task and report an exhaustive evaluation of the systems participating in the task organized at SemEval-2007. The aim of this task is to provide an evaluation where the sense inventory is not predefined and where performance on the task would bode well for applications. The task not only reflects WSD capabilities, but also can be used to compare lexical resources, whether man-made or automatically created, and has the potential to benefit several natural-language applications.

We propose a multilingual unsupervised Word Sense Disambiguation (WSD) task for a sample of English nouns. Instead of providing manually sensetagged examples for each sense of a polysemous noun, our sense inventory is built up on the basis of the Europarl parallel corpus. The multilingual setup involves the translations of a given English polysemous noun in five supported languages, viz. Dutch, French, German, Spanish and Italian. The task targets the following goals: (a) the manual creation of a multilingual sense inventory for a lexical sample of English nouns and (b) the evaluation of systems on their ability to disambiguate new occurrences of the selected polysemous nouns. For the creation of the hand-tagged gold standard, all translations of a given polysemous English noun are retrieved in the five languages and clustered by meaning. Systems can participate in 5 bilingual evaluation subtasks (English- Dutch, English- German, etc.) and in a multilingual subtask covering all language pairs. As WSD from cross-lingual evidence is gaining popularity, we believe it is important to create a multilingual gold standard and run cross-lingual WSD benchmark tests. 1

Word sense disambiguation is typically phrased as the task of labeling a word in context with the best-fitting sense from a sense inventory such as WordNet. While questions have often been raised over the choice of sense inventory, computational linguists have readily accepted the bestfitting sense methodology despite the fact that the case for discrete sense boundaries is widely disputed by lexical semantics researchers. This paper studies graded word sense assignment, based on a recent dataset of graded word sense annotation. 1

The vast majority of work on word senses has relied on predefined sense inventories and an annotation schema where each word instance is tagged with the best fitting sense. This paper examines the case for a graded notion of word meaning in two experiments, one which uses WordNet senses in a graded fashion, contrasted with the “winner takes all ” annotation, and one which asks annotators to judge the similarity of two usages. We find that the graded responses correlate with annotations from previous datasets, but sense assignments are used in a way that weakens the case for clear cut sense boundaries. The responses from both experiments correlate with the overlap of paraphrases from the English lexical substitution task which bodes well for the use of substitutes as a proxy for word sense. This paper also provides two novel datasets which can be used for evaluating computational systems. 1

The computation of meaning similarity as operationalized by vector-based models has found widespread use in many tasks ranging from the acquisition of synonyms and paraphrases to word sense disambiguation and textual entailment. Vector-based models are typically directed at representing words in isolation and thus best suited for measuring similarity out of context. In his paper we propose a probabilistic framework for measuring similarity in context. Central to our approach is the intuition that word meaning is represented as a probability distribution over a set of latent senses and is modulated by context. Experimental results on lexical substitution and word similarity show that our algorithm outperforms previously proposed models. 1

Data sparsity is one of the main factors that make word sense disambiguation (WSD) difficult. To overcome this problem we need to find effective ways to use resources other than sense labeled data. In this paper I describe a WSD system that uses a statistical language model based on a large unannotated corpus. The model is used to evaluate the likelihood of various substitutes for a word in a given context. These likelihoods are then used to determine the best sense for the word in novel contexts. The resulting system participated in three tasks in the SemEval 2007 workshop. The WSD of prepositions task proved to be challenging for the system, possibly illustrating some of its limitations: e.g. not all words have good substitutes. The system achieved promising results for the English lexical sample and English lexical substitution tasks. 1

In this paper we describe the SemEval-2010 Cross-Lingual Lexical Substitution task, where given an English target word in context, participating systems had to find an alternative substitute word or phrase in Spanish. The task is based on the English Lexical Substitution task run at SemEval-2007. In this paper we provide background and motivation for the task, we describe the data annotation process and the scoring system, and present the results of the participating systems. 1

This paper describes a set of exploratory experiments for a multilingual classificationbased approach to Word Sense Disambiguation. Instead of using a predefined monolingual sense-inventory such as WordNet, we use a language-independent framework where the word senses are derived automatically from word alignments on a parallel corpus. We built five classifiers with English as an input language and translations in the five supported languages (viz. French, Dutch, Italian, Spanish and German) as classification output. The feature vectors incorporate both the more traditional local context features, as well as binary bag-of-words features that are extracted from the aligned translations. Our results show that the ParaSense multilingual WSD system shows very competitive results compared to the best systems that were evaluated on the SemEval-2010 Cross-Lingual Word Sense Disambiguation task for all five target languages. 1

In this paper we analyse data from the SemEval lexical substitution task in those cases where the annotators indicated that the target word was part of a phrase before substituting the target with a synonym. We classify the types of phrases that were provided in this way by the annotators in order to evaluate the utility of the method as a means of producing a gold-standard for multiword evaluation. Multiword evaluation is a difficult area because lexical resources are not complete and people’s judgments on multiwords vary. Whilst we do not believe lexical substitution is necessarily a panacea for multiword evaluation, we do believe it is a useful methodology because the annotator is focused on the task of substitution. Following the analysis, we make some recommendations which would make the data easier to classify. 1.