## 3 State of the Art  
### IFM Framework  
The IFM Framework originates from cross-disciplinary research into the abstract visualization and representation of a system and its functionality to permit the linking of different, discipline-specific perspectives into design in one common model. It provides a modeling approach describing the functionality of a system that is coupled with a structural modeling approach of this system. The IFM Framework uses an understanding of function as the intended behavior of a technical system that it needs to exhibit to fulfil its purpose. In the framework, integration is enabled by means of linking different types of contents, which are usually addressed in discipline-specific and cross-disciplinary function models. For instance, the intended behavior can be modeled as distinct (transformation) processes describing relevant activities and steps, states and their changes through the shown behavior and so forth (see Table 1), where different disciplines are known to favor one over the other [17]. The respective pieces of information that describe the functionality from a distinct viewpoint are presented in different views, which are briefly described in Table 1. The system's overall functionality is thus represented through the combination of views, each describing function through specific descriptors: the process flow view describes functionality as a sequence of (transformation) processes, the state view describes functionality through consecutive state changes, etc. The adjacent placement of the six views (see Figure 4) supports their parallel development. The adjacent placement also enables verification of whether the views are mutually consistent. Views are modular and may be added or omitted depending on whether or not they are required by the designers involved in a specific development project at hand. This permits flexible, demand-specific tailoring of the framework to match modeling demands and preferences. Figure 4: The IFM Framework. Reprinted with permission from [17]. The process flow view, which is placed in the center (Figure 4), visualizes the flow of transformation and interaction processes using common arrow-type modeling to indicate temporal sequence (or parallelism) between individual processes. The remaining views comprise matrices equivalent to the well-known design structure matrices (DSM) and encompass the remaining entities, which are related to the functionality of the system, and their interdependencies. Entities comprise use cases, transformation and interaction processes, states and effects as well as operands and actors. Each of these entities (within their dedicated view, as outlined in Table 1) is logically linked to the processes in the centrally placed process flow view. As will be illustrated further down, what this effectively means is that, for every process, the state view will provide the states and their changes related to it. The actor view illustrates which specific abstract function carriers (technical sub-systems, parts or animate beings) will carry out the specific process and state changes, respectively, and so forth. Together, all views and their contents permit the designers to visualize all facets of a system's functionality in a systematic and logically interlinked matter, without requiring the use of specialized software environments. Use cases, as an entity in the framework, represent different scenarios or sequences of events that describe the application of the technical system for a specific purpose; to illustrate, a smartphone may be used for making calls, writing text messages, accessing the internet and so much more--in the IFM Framework, each of these scenarios would be considered a different use case, and very different functionality is required to realize each of them. Transformation processes describe processes of technical and/or human origin that result in a change of the state of either operands or actors for every use case. The