# Towards Hierarchical Workflows in SysML to Support Virtual Validation of Technical Systems
## 2 State of the Art  
### Function-Oriented System Architecture  
More and more practical MBSE methods are proposed [6; 7; 8] and applied to the design and validation process of real-world technical systems, such as the telescope system [9], the aero-engine system [10], the space system [11], and the wind turbine system [12]. For this research, a more detailed and comprehensive MBSE method proposed by [PERSON] et al. [6] for function-oriented system development was chosen. On the one hand, the merit of this method lies in its ability to offer transparent traceability by constructing clear relationships within the system architecture, connecting requirements, functions, and the solution layer responsible for functional fulfillment during development processes. On the other hand, this method is able to integrate domain models from diverse engineering disciplines, going beyond merely remaining at the conceptual design stage. This method lays the foundation to significantly improve the practicality of MBSE in developing technical engineering systems [6]. Motego, as a function-oriented modeling approach that provides a specific SysML profile for technical engineering systems, is introduced in the following paragraphs. A successful system is developed to fulfill the requirements of stakeholders. Therefore, the significant task of system modeling is to collect and model these requirements before and during the development process of the system. In the Motego modeling approach [13], the requirements are mainly classified into two types: functional requirements and design requirements. Functional requirements outline the necessary functions and behavioral aspects for a system to operate effectively [14]. In Motego, requirements are linked to other SysML elements (e.g., the value properties) through different relationships, such as satisfy and validate relationships. Functional requirements depict the desired functional behavior, which can be virtually confirmed through functional testing, drawing on corresponding solutions. Design requirements, on the other hand, are directly met by the property values present in the solutions. Functions can be derived from functional requirements. They are linked to corresponding requirements of systems through satisfy relationships. The functional architecture is in the form of a hierarchy. As shown in Figure 1, the primary function can be broken down into sub-functions, which act as components of a single higher-level function. A system function, or a portion of it, can be defined by a boundary that allows physical quantities to pass in and out as functional flows. These flows may consist of energy, materials, or signals. The function of the delimited system converts the incoming flow quantities into different outgoing flow quantities. If the transformation of the flows they represent cannot be further decomposed, functions are termed as elementary functions. Solution describes a general effect with geometry or a set of general effects that fulfills functions physically. The functions and the solutions are linked by generalization relationships. Therefore, the solutions will inherit the functional flows from the functions they fulfill. Moreover, system solutions consist of hierarchically structured sub-system solutions, with their parameters interconnected across various hierarchy levels. A system solution is referred to as a solution element if it does not physically decompose further. A solution element consists of the physical effects and more parts, such as active surface pairs. Domain models are incorporated into the system model to further describe the related solution's physical behavior. Each domain model is enclosed within a SysML constraint, featuring input and output ports that connect with external domain simulation models. The constraints are connected to the parameters of the corresponding solution. High-fidelity domain models are seamlessly linked with the structured solution to ensure changes can be propagated into the domain models.