A system model is the conceptual model as a result of system modeling that describes and represents a system. A system comprises multiple views such as planning, requirement (analysis), design, implementation, deployment, structure, behavior, input data, and output data views. A system model is required to describe and represent all these multiple views.
The system model describes and represents the multiple views possibly using two different approaches. The first one is the non-architectural approach and the second one is the architectural approach.
The non-architectural approach respectively picks a model for each view. For example, Structured Systems Analysis and Design Method (SSADM), picking the Structure Chart (SC) for structure description and the Data Flow Diagram (DFD) for behavior description, is categorized into the non-architectural approach.
The architectural approach, instead of picking many heterogeneous and unrelated models, will use only one single coalescence model. For example, System architecture, using the Architecture Description Language (ADL) for both structure and behavior descriptions, is categorized into the architectural approach.