## 3 Results
### Comparison and Correlation  
In the following section, two portfolios are derived from above-stated findings of the literature analysis in order to compare and correlate results (Table 3, Figure 5). In combination, they give a complete overview of relevant characteristics for the pursued objectives (Findings 3, 8, 9). Technical systems (Finding 6: need for engineering), product service systems and further environment are considered means of value creation (Finding 1) in both portfolios and, therefore, span the abscissa. As multi-disciplinarity is implicitly assumed but not concretized in many approaches, no further separation into single- and multi-disciplinary technical systems is taken. Product-service systems represent a combination of material core products with affiliated services during operations [52]. Although \"further environment\" is not relevant to the problem at hand in the narrow sense, it allows a view beyond the horizon. Thus, it forms a basis for the plausibility check. It extends value creation to the life cycles of, for instance, assets, factories, buildings or even food production. The compared lifecycle models are numbered uniformly in both portfolios in chronologic order and mapped to the references listed in Table 3.  
The ordinate of portfolio 1 (Figure 5a) is spanned by way of cross-linking life cycle phases among each other, and it represents the historical evolution from linear to circular modeling (Findings 2, 5). The representation of lifecycles in a linear form reflects the currently still prevailing principle of the linear economy or throwaway economy. Raw materials are used to manufacture products that are disposed of in landfills or incinerated after use. Only a small percentage is put to reuse. This linear economic model contradicts planetary boundaries and the idea of sustainability. However, the objective of modern CE is to minimize resource consumption, waste production, and emissions as well as  
Figure 5: Lifecycle portfolios focusing on technical systems, product-service systems and further environment with regard to product classes (light blue dots) and including instances (dark blue dots): (**a**) categorization differentiating linear and circular models; (**b**) categorization differentiating purely conceptual sequence models and models with specific focus on either information or material flow. energy waste. Energy and material cycles are slowed down, reduced and closed for this purpose. This can be achieved through design for durability, maintenance, repair, reuse, remanufacturing, refurbishing and recycling [67, 68]. Figure 5a shows that linear lifecycle models are still prevailing. They are applied to technical systems (field A), product-service systems (field B) and further environment-emphasizing production systems (field C). Besides mechanical products, further single disciplines are taken into account. For example, [PERSON] et al. assign tasks of integrated development of IT services to lifecycle phases in a linear model [69] (13 in field A). \"Circles as design element\" (fields D, E, F) are a preliminary stage of circular lifecycle models, as they use the circular shape as a metaphor, but in terms of content they still adhere to a linear sequence of lifecycle phases. Circular lifecycle models primarily represent material flows (field G). Only [PERSON] et al. [30] (40 in field G) focus on information capture about product use and [PERSON] et al. [29] (4 in field G) represent information flows along the product life but neglect material flows. The approach of the Ellen MacArthur foundation [59] (36 in field I) comprises the consumer and user's viewpoints and thus, even includes food production. Whereas several product life cycle models for product-service systems already use circles as design elements (field E), there are no detailed circular approaches for technically demanding multidisciplinary systems available (fields G, H).