Numerous abbreviations are used routinely throughout such texts and identifying their meaning is critical to understanding of the document. The problem is that abbreviations are highly ambiguous with respect to their meaning. For example, according to UMLS 2 (2001), RA may stand for “rheumatoid arthritis”, “renal artery”, “right atrium”, “right atrial”, “refractory anemia”, “radioactive”, “right arm”, “rheumatic arthritis,” etc. Liu et al. (2001) show that 33% of abbreviations listed in UMLS are ambiguous. .
