Alexandros Kaliontzoglou Pelagia Boutsi Despina Polemi eInvoke: Secure e-Invoicing based on web services. 337-353 2006 6 Electronic Commerce Research 3-4 http://dx.doi.org/10.1007/s10660-006-8678-6 db/journals/ecr/ecr6.html#KaliontzoglouBP06