## 3 Results
### Literature Analysis
#### 3.1.1 Specific Perspectives (Subjects)  
Lifecycle perspectives are present in all disciplines that target technical solutions. In mechanical engineering, the main perspective lies in the Product Lifecycle: typical phases are product planning, development, realization, distribution, use and recycling [28; 29]. Development covers both the development of the product and planning of the required production process to realize product instantiation. Beginning of Life (BoL) of an individual product instance is characterized by its production, Mid of Life (MoL) represents the use phase and End of Life (EoL) can be understood as a synonym for recycling [30]. Product Creation is starting with a clear product idea and development order [31; 32]. The term is either used for the entire BoL [28] or covering the creation of the product definition exclusively, without execution of production [33]. These models are focused on product classes and production systems to instantiate them in terms of tangible manifestations. Product instances resulting from this production process are only implicitly assumed in the phase \"manufacturing of parts\" (see Figure 2a [31]). To enable production, plants have requirements according to their specific lifecycle perspective: design, building, ramp-up, operation and teardown [34]. Similar perspectives are stated for technical assets [35]. Instances are made from material, which are brought in as raw material or recycled from preceding products. Additionally, energy supply is an essential input (see Figure 2b [36]; cf. [37]). In software engineering, lifecycle phases range from specification, design, implementation, installation/deployment to use and removal [38; 39]. Specific attention is paid to the continuous evolution of software products during their lives [40; 41] (see Figure 2c). Another specific perspective is defined for services: service lifecycle phases cover service planning, design, implementation, delivery and decommission [42]. Focusing on learning aspects throughout service life, overarching phases of service design (before implementation) and service management can be differentiated [43] (based on [44]). From these models presented in very brief summaries, several findings are deduced that have to be considered when integrating disciplines and domains. **Finding 1. **_All specific perspectives are focused on value creation as a key objective._  
Lifecycles are triggered by problems, needs or tasks. Material core products, services and software are engineered single-, inter- or multi-disciplinarily and realized to provide value in the operation phase. In CE, even the EoL phase is viewed from the perspective of value creation. Extending that perspective to sustainability, value is envisioned with respect to economics, ecology and society. **Finding 2**. : _Models are visualized either by cycle or chain metaphor._  
Cycles as such are highlighted in some of the models, chains are often used for the purpose of simplification. In many cases there is no clear indication whether the visualization is dedicated to logical, information/material flow or temporal dependencies. **Finding 3**. : _Focusing on different disciplines, a transparent differentiation of product classes and instances is essential. Especially when it comes to material, volumes are important in phases focused on product instances._  
Analogous to product modeling, the specification of product classes is the required basis for instantiation in terms of individual product instances. This is a prerequisite to deal with the circularity of resources, i.e., material and information. In the case of material core products, instantiation takes place during production. Based on the product class specification and out of the delivered source material (raw and/or recycled), individual product instances are manufactured and assembled. In the case of software, instantiation happens with its installation, deployment or activation.