nd hearing about historic failures and near misses have always held a special fascination for me. Human- kind's ingenuity and imagination does indeed seem unlimited and its willingness to experiment endless. While bemused, I am also comforted by the knowledge that today, the physics underlying these things is well understood. Armed with this understanding, our architects and engineers are now able to create models to simu- late all sorts of scenarios, allowing them to validate their designs and assumptions. When, on the other hand, it comes to networks and systems, we still tend to cre- ate them writing one line of code at a time. Yes, modelling is beginning to take on a greater importance, but it still remains at the software component level. So where is the architecture in today's systems and networks? What ensures that the total is more than just the sum of the components? I had the fortune and great pleasure to work with Thomas Muth for the two years he was on contract in Montreal. As a result of our frequent discussions, I not only got to know and understand the principles of systems modelling, but also found a framework and a place holder for many of the ideas and concepts that I had always known to be fundamental and imperative to good design. Needless to say I also found a friend. Foreword I have always had the feeling that there was something essential missing in UML and other notations, but I was unable to put my finger on it until I understood the significance of what Thomas calls "sysnet", which finds expression in Sysnet Modelling (SM), supported by the Abstract systems Modelling Language (AML). Sysnet modelling deals with principles for modelling complex systems. Sysnet modelling is independent of the modelling language and notation used, be it AML or any other modelling language and notation. The concept "sysnet" provides a clear understanding of the distinction between "problem space" and "solution space". Creating and defining an architectural notation and language is not only a daunt- ing task t