From this page you can access the viewer software that is referred to in the following publications:
N.J. van Eck, L. Waltman, and J. van den Berg. A novel algorithm for visualizing concept associations. In Proceedings of the 17th Belgian-Dutch Conference on Artificial Intelligence, pages 397-398, 2005.
N.J. van Eck, L. Waltman, and J. van den Berg. A novel algorithm for visualizing concept associations. In Proceedings of the 16th International Workshop on Database and Expert Systems Applications, pages 405-409, 2005.