We have been inquiring into the relationship between systems, knowledge domains and engineering, triggered by the challenges of integrating domain-specific modelling tools with overall systems models. A simple initial realization was that a distinctive characteristic of software and systems engineering, as compared to other engineering disciplines, is that correctness of solutions in these disciplines depends to a large extent on the body of knowledge in other fields. Perhaps this is why it has proven harder to create theoretical foundations that explain engineering practice in these disciplines, resulting in their being viewed widely as empirical disciplines.

Our inquiry led us to realize that knowledge domains can be categorized into knowledge domain that focus on wholes (e.g. network routers), and knowledge domains that focus on aspects (e.g. network routing). Wholes knowledge include knowledge about how wholes relate to aspects, as well as how they relate to other wholes.  They carry the knowledge that enables multiple knowledge disciplines to come together in systems. This insight suggests a modular approach to knowledge representation (modular ontologies) with bridges that establish linkages among them based on their relative roles in the system of interest.