  Architecture Definition, which is central to system design, is one of the two
most used technical processes in the practice of model-based systems
engineering. In this paper a fundamental approach to architecture definition is
presented and demonstrated. The success of its application to engineering
problems depends on a precise but practical definition of the term
architecture. In the standard for Architecture Description, ISO/IEC/IEEE
42010:2011, a definition was adopted that has been subsumed into later
standards. In 2018 the working group JTC1/SC7/WG42 on System Architecture began
a review of the adopted definition, holding sessions late in the year. This
paper extends and complements a position paper submitted during the meetings;
in which Tarski model theory and ISO/IEC 24707:2018 (logic-based languages)
were used to better understand relationships between system models and concepts
related to architecture. Independent from the working group, it now contributes
intuitive fundamental definitions of the terms architecture and system that are
used to specify a mathematically based technical process for architecture
definition. The engineering utility and benefits to complex system design are
demonstrated in a diesel engine emissions reduction case study.
