The problem of ambiguous words (words are hereinafter referred to as terms) in the
context of information retrieval (IR) is illustrated in Figure 1.1. The user in this case, is
trying to find information about Christmas trees. Mentally the user thinks of Christmas
tree in the context of celebrating Christmas (i.e. a holiday held to commemorate the
birth of Jesus, a central figure in Christianity). The user formulates a query that is
submitted to a search engine. In a traditional search engine the query terms are matched
with the terms in an inverted index consisting of all the document terms of a text corpus
(Baeza-Yates & Ribeiro-Neto, 1999). Only matched documents are retrieved and