Tomorrows systems will be based on close interactions of mechanics, electrics/electronics, control engineering, sofhvare technology, or new materials, as well as possessing inherent intelligence that will make them superior to mechatronics. Their main features are adaptability, robustness, and proactivity. Intelligent systems are multidisciplinary and therefore, they need to be developed in a discipline-spanning manner. Two targets arising from this are on the one hand a consistent superordinate process model, and on the other hand an appropriate support for this process model with sufficient methods. One step towards reaching those targets is more formalization in systems engineering for traditional engineering. A systematic use of different requirement levels in a given development process is displayed in this contribution. It is shown that, when interpreted in the right way, requirements provide one option to interconnect the different phases inside this development process. Four levels of requirements are defined and allocated to a development process. For a process model's applicability, it is beneficial to provide supporting methods. We discuss certain methods for the different development phases of the V-model. Starting with goals of the development, the evolution from goals towards functions and systems is described via enriched partial models, which provide an early description of the system behavior. The interactions of the partial models with the requirement levels are described to increase consistency between requirements, functions and system elements. A benefit emerging with this is the advantageous traceability of requirements. To formalize requirements connections to the system, an analysis method is presented, which quantifies connectivity of each element, as well as the degree of connections inside the entire system. Hence, the possibilities of examining the connections between requirements, goals and system elements are expanded.