# Systematic Literature Review of System Models for Technical System Development
## 4 Discussion
### Drivers and Indicators for the Usage of System Models
* _System Certification:_ The publications explicitly mentioning certification as a driver see system modeling not only as a means to satisfy other certification requirements, but also as a direct requirement by certification authorities. * _System Performance:_ This driver does not relate to the implementation of novel features but improvements in non-functional properties, like general efficiency of the system, uptime, or accuracy of an operation executed by the developed system. * _Collaboration:_ A number of publications mention general collaboration among developers or even all stakeholders as a driver. This often is related to the ease or efficiency of exchange of information and data between developers internally, as well as with customers and other external parties. Indicators:
* _Improved Modeling Quality:_ This indicator includes factors such as model fidelity and performance in other aspects. * _Earlier Testing and Validation:_ This relates to the front-loading of verification and validation activities. * _Traceability:_ This includes explicit traceability, e.g., in a requirements engineering context, as well as (dynamic) modeling of connections inside and between models improved systems. * _Integration:_ This includes aspects such as (co-) simulation and other digital methods that allow for front-loading and concurrent execution of integration activities. * _Better Requirements:_ This indicator relates to improved requirements in terms of the formal quality of the developed requirements and their usefulness for other aspects of system development. * _Improved Tools and Methods:_ This comprises improved IT-Tools and methods enabled by the application of systems modeling. * _Compliance:_ This indicator indicates a direct requirement to apply systems modeling by certification bodies or legal frameworks. * _Better Solution Architecture:_ An improved solution architecture relates to an improved system in terms of features available and/or system performance through new structural or behavioral properties that emerged using systems modeling. * _Intellectual Property (IP):_ This indicator relates to the way that system models can support the protection of intellectual property, in this particular case through compartmentalization of IP and easier exchange of subsystem models. Our analysis shows that the general challenge of development processes, system quality and system complexity are the main drivers for the application of system models (combined those three alone amounts to more than 73% of all mentions). These three are not necessarily independent criteria and over the course of our review, we come to conclude that the main reason development processes are perceived as challenging is often a combination of system complexity and the complexity of processes and tools. This would suggest that managing complexity and achieving high quality are the key drivers for the use of system modeling. The fact that complexity is a vaguely defined term in the context of systems engineering appears to show a relatively equal distribution of connections to all  
Figure 11: Sankey-flow chart with drivers depicted on the left side and indicators on the right. mentioned indicators. The three largest drivers System Complexity, Development Process and System Quality account for an overwhelming majority among the drivers. They are associated with almost all indicators to equal amounts (with the exception of System Quality being biased towards improved model performance), which may be because system development of large and interconnected systems poses a particular challenge with wide-ranging impact. This is because it comprises various activities and technical goals, which need to be managed and balanced in order to create the desired system or at least approximate the ideal outcome as closely as possible with available resources and under the current circumstances.