Y. Kalfoglou, and W. Schorlemmer. Proceedings of the 13th International Conference on Conceptual Structures (ICCS 2005), volume 3596 of Lecture Notes in Computer Science, page 107-118. Springer, (2005)
J. Goguen. Proceedings of the 13th International Conference on Conceptual Structures (ICCS 2005), volume 3596 of Lecture Notes in Computer Science, page 52-77. Springer, (2005)