## 3 Results
### Comparison and Correlation
In addition to the lifecycle approaches illustrated in Figure 5, [PERSON] presents the service lifecycle as a circle consisting of linear representations of service design and service management. However, he does not consider entire product-service systems and, therefore, is not included in the portfolios [43] (referring to [44]). According to Finding 2 \"Models are visualized either by cycle or chain metaphor\", portfolio 2 classifies the lifecycle models' degree of detail (Figure 5b) from an overview illustration named \"conceptual sequence\" to a detailed model comprising information and/or material flows (Finding 8). The conceptual sequence includes both logical and temporal dependencies in the flow logic (Findings 4, 7). Obviously, many conceptual sequences are found for all means of value creation: most apply to single-disciplinary or not further specified technical systems (field J), others apply to product-service systems (field K) and several to further environment (field L). Among these, only [PERSON] and [PERSON] explicitly emphasize interdisciplinary [15, 33] (17 in field K). Their model comprises mechanics, electronics, software and even services. However, this approach serves as a visual model and, therefore, stays on a conceptual sequence level. Neither information nor material flows are concretized in detail. In sum, only few lifecycle models already address information or material flows (fields M, P, Q and R). Except for [PERSON] 2013 [43] (30 in fields N and Q), no further lifecycle model addresses \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**No.** & **Authors** & **Ref** & **No.** & **Authors** & **Ref** & **No.** & **Authors** & **Ref** \\ \hline
1 & [PERSON] 1991 (2002) & [70] & 22 & [PERSON] et al., 2010 & [71] & 43 & [PERSON] 2016 & [58] \\
2 & VDI 2243:1993 & [72] & 23 & [PERSON] et al., 2011 & [73] & 44 & VDI 4800:2016 & [74] \\
3 & VDI 2221:1993 & [75] & 24 & [PERSON] and [PERSON] 2011 & [38] & 45 & [PERSON] et al., 2017 & [61] \\
4 & [PERSON] et al., 1996 & [29] & 25 & [PERSON] et al., 2011 & [76] & 46 & [PERSON] 2017 & [77] \\
5 & [PERSON] et al., 2000 & [41] & 26 & [PERSON] 2011 & [39] & 47 & European Union 2017 & [37] \\
6 & [PERSON] et al., 2000 & [78] & 27 & [PERSON] et al., 2012 & [79] & 48 & [PERSON] et al., 2017 & [51,80,81] \\
7 & [PERSON] 2002 & [35] & 28 & [PERSON] et al., 2012/ 2017 & [82] & 49 & [PERSON] et al., 2017 & [82] \\
8 & VDI 2243:2002 & [83] & 29 & [PERSON] et al., 2012 & [84] & 50 & [PERSON] 2017 & [85] \\
9 & [PERSON] 2004 & [86] & 30 & [PERSON] 2013 & [43] & 51 & [PERSON] et al., 2018 & [31] \\
10 & Schenk and With 2004 & [34] & 31 & [PERSON] 2013 & [87] & 52 & [PERSON] et al., 2018 & [35] \\
11 & [PERSON] et al., 2005 & [88] & 32 & Thomas and Nuttgross 2013 & [89] & 53 & VDI 4801:2018 & [90] \\
12 & [PERSON] et al., 2006 & [54] & 33 & [PERSON] 2014 & [91] & 54 & [PERSON] et al., 2018 & [46] \\
13 & [PERSON] et al., 2005 & [69] & 34 & [PERSON] 2014 & [92] & 55 & [PERSON] et al., 2019 & [40] \\
14 & [PERSON] 2008 & [93] & 35 & [PERSON] and Stoffels 2014 & [94] & 56 & [PERSON] et al., 2019 & [68] \\
15 & [PERSON] 2008 & [95] & 36 & E. MacArthur Edt. 2015 & [59] & 57 & [PERSON] et al., 2019 & [36] \\
16 & [PERSON] et al., 2009 & [96] & 37 & [PERSON] and Hedberg, 2015 & [97] & 58 & [PERSON] et al., 2019 & [98] \\
17 & [PERSON] et al., 2009 & [33] & 38 & [PERSON] et al., 2015 & [99] & 59 & [PERSON] et al., 2019 & [100] \\
18 & [PERSON] et al., 2009 & [66] & 39 & [PERSON] et al., 2015 & [101] & 60 & VDI 222:219 & [28] \\
19 & [PERSON] 2009 & [57] & 40 & [PERSON] et al., 2015 & [30] & 61 & [PERSON] et al., 2020 & [102] \\
20 & [PERSON] et al., 2010 & [103] & 41 & [PERSON] et al., 2016 & [101] & 62 & [PERSON] et al., 2020 & [104] \\
21 & [PERSON] et al., 2010 & [64] & 42 & [PERSON] et al., 2016 & [42] & 63 & [PERSON] et al., 2020 & [105] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chronological listing of lifecycle identified in literature. both linkages: information and material flows. Nevertheless, this approach represents a linear lifecycle model.