1. Burdett, D. Internet Open Trading Protocol Version 0.9.9. The Open Trading Protocol Consortium, 1998.
2. Christoffel, M. Pulkowski, S., Schmitt, B., Lockemann, P. Electronic commerce: the roadmap for university libraries and their members to survive in the information jungle. ACM Sigmod Record, 27 (4), 1998, pp. 68–73.
3. Christoffel, M. A trader for services in a scientific literature market. In Proceedings of the 2nd International Workshop on Engineering Federated Information Systems (EFIS’99), Kühlungsbom, 1999, pp. 123–130.
4. Hewlett Packard. E-Speak - the platform for E-services.
http://www.e-speak.hp.com
5. IBM. DB2 Digital Library.
http://www-4.ibm.com
software/is/dig-lib/about.html.