## 6 Discussion  
This study presents an ontology-based development approach to developing SoS architecture that covers strategic and operational domains. The approach provides a systematic presentation of multiple perspectives and construction procedures to assist in developing architecture models. Although the strategic domain is addressed first, it is closely interrelated with the operational domains of operations, resources, projects, and others. Thus, after analyzing the other domains, revisiting the strategic domain to revise traceability and conduct further analysis becomes necessary. For instance, insufficient domain knowledge in the strategic domain can be improved by constructing the operational architecture. The operational high-level concept diagram can help domain experts comprehend the mission decomposition. The traceability mechanism enables the appropriate implementation of capabilities and facilitates analyzing the effects of changes [43]. This study presents a series of architectural steps that enable traceability among various entities, including mission and capability, capability and operational role, and capability and operational activity. However, the traceability between assigned capability and corresponding CSs may require additional UAF domains, such as resource (Rs), criteria/standard (Sd), and actual resources (Ar), which could be considered in future work. Compared with the ontology-based method for the breakdown of SoS missions [18], which uses the UAF at the model level before reasoning based on ontology, this study develops ontology at the metamodel level, thus providing more flexibility for the SoS modeling based on AFs. Ontologies can help to avoid ambiguities, facilitate information exchange between modules and external software, and provide a shared understanding of the design process [59]. In contrast to an ontology-based common conceptual reference used as a foundation for aircraft design processes [59], we employ the UAF metamodel to develop an ontology with greater detail on the SoS architecture. This enriched ontology extends the relationships and flows, facilitating the proposal of architecture steps. Unlike the semantic approach [60] that seeks to resolve regulatory ambiguity in aircraft design  
Figure 20: Operational States (Op-St) of operational performers. and development through process mapping, Unified Modeling Language (UML), and ontological modeling, we present a set of specific architectural steps that offer simplicity and ease of use. The conceptual methodology for SoS development provides six steps to select the preferred SoS [61] but does not implement the modeling process by any architecture description language. This paper provides detailed steps based on ontology using the UAF views implemented by SysML. The flow-based functional analysis is applied at the system level [58], and the flow-based design process is expected to be used in individual standalone systems [55]. This study introduces architectural steps at the SoS-level, which can be upstream of the system design in SE. The SoS modeling process in this paper is considered to develop SoS architecture based on AFs [13]. The development of architecture models involves selecting from more than 80 views supported by AFs and building them in a proper sequence. Therefore, the essential model elements in views such as mission, capability, and operational aspects should be explicitly described, and their organization and consistency should also be carefully considered. In particular, organizing elements meaningfully ensures explicit relationships between views within viewpoints. Better consistency among elements can improve communication and understanding among stakeholders. Therefore, relationships between views can be more explicit, and the modeling sequence can be more precise. Table 4 compares the proposed approach in this paper with three other studies regarding the descriptions of architectural elements and the consistency between them.