P. Chapman, G. Stapleton, J. Howse, and I. Oliver. 2011 IEEE Symposium on Visual Languages and Human-Centric Computing (VL/HCC), page 87-94. (September 2011)
J. Howse. Proceedings of the 16th International Conference on Conceptual Structures (ICCS 2008), volume 5113 of Lecture Notes in Computer Science, page 1-20. Springer, (2008)