## 2 Background
### Kano Model  
The Kano model, developed in 1984, is based on [PERSON]'s motivation-hygiene theory (1968) and the law of diminishing marginal utility. It considers the subjective aspects of satisfaction and dissatisfaction, and the objective aspect of functionality [20]. The role of quality can be classified into five categories, according to the degree with which acceptance and satisfaction are provided to users, and using a classification form based on the two dimensions of the Kano model:  
1. Attractive quality attributes (A): A sufficient conditional quality attribute that provides satisfaction when achieved fully, but that does not cause dissatisfaction when unfulfilled;
2. One-dimensional quality attributes (O): A necessary conditional quality attribute that results in satisfaction when fulfilled, and dissatisfaction when unfulfilled;
3. Must-be quality attributes (M): A necessary attribute that, if not fulfilled, will cause customer dissatisfaction; however, if it reaches a certain level, the customer is no longer satisfied;
4. Indifferent quality attributes (I): A quality attribute that does not significantly affect customer satisfaction, regardless of whether it is fulfilled;
5. Reverse quality attributes (R): A quality attribute that, if fulfilled, causes dissatisfaction and, if unfulfilled, it satisfies the customer. The attributes in the Kano model can be primarily classified using questionnaires; an exemplary questionnaire is shown in Table 1 below. The Kano questionnaire presents a pair of questions (a functional form and a dysfunctional form) for an acceptance element, and the acceptance element is classified as one of the five dimensions, according to the answers. The classification criteria are summarized in Table 2 below. However, because the quality attribute classification under the Kano model is judged to be the most frequent quality attribute, relatively weaker quality attributes are ignored. To address these issues, the customer satisfaction coefficient presented by [PERSON] (1993) was used to calculate the impact of the customer satisfaction and dissatisfaction (2011). The customer satisfaction coefficient determines the degree of user satisfaction or dissatisfaction when a user uses a product or service; it can be derived by calculating the frequencies corresponding to the following quality attributes:  
\[\text{SI}:\,\text{Satisfaction Index}=\frac{A+O}{A+O+M+I} \tag{1}\]  
\[\text{DI}:\,\text{Dissatisfaction Index}=(-1)\bigg{(}\frac{O+M}{A+O+M+I}\,\bigg{)} \tag{2}\]  
The factors perceived to be more important can be predicted; then, from these, it is advantageous to classify the quality attributes into the necessary conditions (e.g., competitive advantage and indifference) for each attribute, and establish development strategies (Figure 2). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{5}{c}{**Dysfunctional form of the Question**} \\ \cline{3-8}  & & **Like** & **Must-Be** & **Neutral** & **Live With** & **Dislike** \\ \hline \multirow{4}{*}{Functional form of the question} & Like & Q & A & A & A & O \\ \cline{2-8}  & Must-be & R & I & I & I & M \\ \cline{1-1} \cline{2-8}  & Neutral & R & I & I & I & M \\ \cline{1-1} \cline{2-8}  & Live with & R & I & I & I & M \\ \cline{1-1} \cline{2-8}  & Dislike & R & R & R & Q \\ \hline \hline \end{tabular} A: Attractive; O: One-dimensional; M: Must-be; I: Indifferent; R: Reverse; Q: Questionable.  
\end{table} 
Table 2: Kano model evaluation table. The Kano model has been applied in various studies to determine the elements that affect user acceptance or satisfaction. [PERSON] et al. used the Kano model to ensure user satisfaction with a function derived as a concept in the development of smart audio [22]. [PERSON] applied the Kano model to evaluate the service quality of sports programs for the elderly [23]. [PERSON] et al.