The notion of fairness is a very general concept and can be used to coin terms in many different application areas. Recently the term fairness has appeared in the context of electronic commerce. Here, the term fair exchange refers to the problem that two parties want to swap some distinct items in a way which ensures that no participant can gain advantage over the other. Many protocols for fair exchange have been proposed but comparing or formally verifying them has remained rather difficult. The reason for this is that the notion of fairness they use is often different, and exact (i.e., formal) fairness definitions do not exist. We make a first attempt to approach a formal definition of fairness in electronic commerce. We do this by reviewing the established terminology regarding the notion of fairness in concurrency theory and adapting the formal apparatus to derive three precisely separable definitions of fairness in electronic commerce which we call strong, eventually strong and weak fairness.
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