After the ontology inclusion and extension of the previous paragraphs, now a more complex projection will be presented, i.e. the projection of the abstract systems theory ontology to the component ontology. The component ontology defines the structural view on physical systems engineers have as depicted in Figure 2, i.e. components that can have subcomponents and terminals. The terminals are the interfaces of the components to the outer world. Therefore, connections hook onto terminals instead of components. This interpretation of components and connections is a bit more complex than the networks of abstract individuals and connections in systems theory. Nevertheless, the definition of these concepts can be kept simple due to a projection of the abstract systems theory on the definitions of engineering components and connections, thus enforcing the components to comply to the rules of systems theory. The paragraph below describes the way this projection takes place. Because this projection makes abstract concepts more specific, this type of projection is called include and specialize.
Figure 6: Excerpt from the component ontology. This ontology formalizes the component view of engineers on physical systems. Note that the ontology can be kept relatively simple because systems theory is projected onto it.
Figure 6 shows some definitions from the component view ontology. The important classes are the classes component, terminal and physical-system. The relations comp.subcomp, comp.term and conn.term relate components to their subcomponents, terminals to components and connections to terminals. Only the definitions contributing to the ontology projection are shown in the figure. Ontology projection consists of inclusion (line 2) and the definition of axioms that specify the abstraction of components to system theoretical concepts. Definition 3 shows how the ontological commitments for abstract mereological individuals are projected onto components. Definition 4 defines the meaning of the comp.subcomp relation in terms of mereology. The projection of topological connections onto component connections is performed by definition 5. Definition 6 defines the modelled device as a system of components. The fact that connections can be of a certain type has been left out of the excerpt to keep it easy to understand.