Information and communication technology (ICT) is applied to support the creation of electronic markets (e-markets). Electronic data interchange (EDI) is the exchange of structured data between information systems of different organizations. EDI is often considered as the first step towards e-markets. In the course of time EDI was extended and interorganizational information systems (IOS) were used to create electronic marketplaces. IOS serve as intermediaries between buyers and sellers. Probably the most well known examples of IOSs are airline reservation systems, which are closed systems having typically a limited number of participants.