## 6 Discussion and Conclusions  
### Research Contribution  
In the last decades, several engineering models were proposed that share the central objective to coherently allow the modeling of functions and solutions [3; 4; 43; 47] (for an overview, see [60]). This follows the increasing digitalization of engineering design processes and the desire to be able grasp the functionality and structure--and their respective interrelations--of a system under development in a single or interrelated model. Such a model would permit the concurrent development and adaptation of what the system is meant to achieve (i.e., its functionality) and how--this is to say, by what technical or human means (i.e., its structure)--it is going to achieve this. The advantages would be substantial in terms of tracking and predicting engineering change efforts, as well as for documentation and behavioral simulation and prediction. From an existing structure, links can be established to prominent engineering simulation tools; thus, by extension, the coherent implementation of a model coupling functional and structural modeling digitally will permit a digital chain from initial functional considerations during conceptual design until engineering simulation in the detail design stages. A rather small number of modeling approaches have been proposed that already link function-oriented modeling with system structural modeling, such as Unified or System Modeling Language (SysML/UML [3; 4; 61]) or Object-Process Methodology (OPM [11]), and also commercial tools, such as Catia (Dassault Systems, Velizy-Villacoublay, France) and many others. However, these approaches are usually rather specific and limited in their scope and/or they are reliant on a particular software environment and a prescribed formalism; in addition, they tend to remain at an abstract level for the description of the resulting technical system, which retains the mentioned barriers between the model and engineering simulation. This paper presents a decisive step forward in this respect using the Integrated Function Modeling (IFM) Framework [17] as a starting point that is to be coupled with structural modeling--fully digitalized--using an executable graph-based modeling language, specifically Design Compiler 43 (DC43). Graph-based languages have the benefit of not being reliant on a specific software environment in visualizing/modeling the content and avoiding so-called \"vendor lock-in\", but, in fact, generate a meta or system model that serves as backend, giving the engineering designer the freedom to choose which specific tools they use to do the actual system modeling in. This may indeed be SysML and other approaches if these are preferred by the designers. In this work, we propose an integration of the IFM Framework with DC43 for the targeted integration of functional and structural modeling. Essentially, we make use of the entities already covered in the IFM Framework and expand the related Entity Relations Diagram strategically to permit the targeted integration, as outlined in Section 4. Specifically, expansions include the addition of a hierarchical requirement structure and detailed object structures that inherit from general classes, e.g., developing geometrical features. One issue arising with this integration might be increased computational costs. However, the information stored in the IFM is mainly relationships between entities that are present in the GBDL anyway and text based small data entities; consequently, this issue is not considered to be critical. Another issue might be the challenge to store a large share of the data and expertise within a unified data model. In current product development processes, these data and expertise are already collected and stored in numerous models, but frequently these models are interconnected and cannot be used to build up an integrated knowledge base. As mainly the interconnections are missing, this issue was also not considered to be critical.