SYSTEMS ARE NOT ONLY SOFTWARE

Hardware and software engineers are called upon to collaborate in building complex high-quality computer-based systems. This paper seeks to facilitate this collaboration by laying foundations for a 'common engineering culture'; a coherent, powerful structure of ideas central to system designers and procurers, with particular relevance to IT systems, hardware and software. We define and formalise the notions of 'system' and 'model', and explore the nature of models of systems in terms of their (quantitatively or qualitatively) measurable properties. We show how the property models of system components combine in the structural model of the system to form the property model of the system as a whole. We also offer illustrative examples from hardware and software to explain the use of models in system specification and design.