# Reasoning Algorithms on Feature Modeling--A Systematic Mapping Study
## 6 Discussion
### Relationships between RQs  
Figure 21 shows a Sankey diagram that represents the relationships that existed between the stages (RQ1), origins (RQ3), validation levels(RQ4), and FMs (RQ5) used so far. The Sankey diagram places a visual emphasis on the transfers or flows within a system. In this case, we refer to how each selected paper responds to each RQ. Next, we present a detailed explanation of these relationships between RQs.  
The first vertical axis represents the stages defined for RQ1, which considers domain engineering (Dom), application engineering (App), and both stages (Dom&App). The second vertical axis represents the origin of proposals defined for RQ3, comprising the academy (Ac), industry (I), and both origins (Ac + I). The third vertical axis represents the validation levelfor each proposal, comprising the categories of evaluation research (EvR), solution proposal (SoP), validation research (VaR), philosophical paper (PhP), and opinion paper (OpP). The fourth and last vertical axis represents the FM representation used.  
The relationship between stages (RQ1) and origins (RQ3) show that 46 papers were associated with the domain engineering category. Thirty-nine were developed in academia, and seven were developed in industry. For the nine papers associated with the application engineering category, four were developed in academia and five in industry. Finally, for the 11 papers associated with both stages, seven were developed by academia and industry, and four were developed jointly by academia and industry.  
The relationship between the origin (RQ3) and validation level(RQ4) shows that 50 papers were associated with the academy category. Twenty of these papers were categorized as evaluation research, fifteen papers were validated as solution proposals, ten papers were classified as validation research, and five papers were validated using the philosophical paper category. Of the twelve papers associated with the industry category, four were validated in the category of evaluation research, three papers were validated as solution proposal, three papers were categorized as validation research, one paper was validated using the philosophical paper category, and one paper was part of the opinion paper category. Finally, the four papers associated with a joint effort (academy + industry) were in the category of validation research.  
The relationship between the validation level (RQ4) and FM (RQ5) shows that 24 papers were associated with the evaluation research category. Five of these papers used extended FM, seventeen papers used FODA, one paper used multiplicity FM, and one paper used  
Figure 21: Relationships between stages (RQ1), origins (RQ3), validation levels(RQ4), and FMs (RQ5).  
a modeling approach classified as \"other\". Of the eighteen papers associated with the solution proposal category, one used extended FM, fifteen used FODA, and two used another modeling notation approach. Of the six papers associated with the philosophical paper category, four used FODA, one paper used multiplicity FM, and one used another modeling notation approach. Finally, one paper associated with the opinion paper category used FODA as its modeling approach.