Post by Giancarlo Guizzardi

Last Friday, my PhD promotor, Professor Christian Anton Vissers, Officer of the Order of Orange-Nassau, passed away. In the photo below, taken during my inaugural lecture for what can be considered a continuation of his chair at the University of Twente, we see a group of people whose ideas he helped to shape directly - from left to right: Luis Ferreira Pires, João Paulo Almeida, Maarten Wegdam, Laura Daniele, Luiz Olavo Bonino da Silva Santos, Marten J. van Sinderen, myself, Nikolay Diakov and, of course, Chris. There are many others missing from the picture (https://lnkd.in/dRm_RQwx) If we go up, rather than down, in his academic tree, we find his PhD supervisor, Gerrit Blaauw (https://lnkd.in/dpW5n-JD), who designed the IBM System/360 together with Fred Brooks (https://lnkd.in/dXPqtWEY) and, via Blaauw, Chris also made us all academic descendants of Howard Aiken (https://lnkd.in/d7hFnHmP). Chris was an engineer, a modeler, and a sculptor (literally!). He had an immense talent for finding the right way of representing things. He was also a philosopher—even his PhD thesis on Interfaces (1977) is fundamentally grounded on a conceptual analysis of that concept. He founded a group that was essentially a unique blend of Conceptual Modeling and Ontology (going under different names) with a strong engineering mindset: of making things practical, of building truly valuable things. Of the many things I learned from him, I highlight three of them here: (1) the importance of getting the concepts right—no amount of bug elimination, whether through formal methods or otherwise, can salvage a bad design; (2) the primacy of real-world semantics (which he called "architectural semantics") over formal semantics—mathematics should serve the conceptualization at hand, i.e., one should never shoehorn the world to fit into one's mathematics; (3) the absolute importance of thinking and writing clearly and precisely. Good writing was for him an act of intellectual courtesy. In the acknowledgements section in my PhD thesis, written 21 years ago, I begin by thanking him: "I am a great admirer of his seriousness towards science and his attitude with respect to understanding things in their essence." Eighteen years later, in my inaugural lecture, I repeated those words to him. He was indeed unswayed by fashion: understanding things in their essence was yet another fundamental lesson we learned from him. After the lecture, he gave me a proud emotional hug - a duplicate of the proud emotional hug he had given me two decades before after my PhD defense. He then also gave me a book of Frisian landscape photos in which he wrote that, since two of my supervisors had come from Friesland (he and Marten van Sinderen), important aspects of being Frisian would have been passed on to me. I hope so, Chris. In any case, your legacy lives on in all of us. RIP in peace, great mentor. Thank you for everything.