## 2 Conceptual Background
### Online Reviews  
As mentioned in Section 2.1, the direct extraction of CA is very important because it is the starting point for establishing a suitable development direction. This is because valid FRs can be derived and further affect the DP in the design phase. Its importance has been further enhanced by diversified competitive products and complicated user needs. When various functions are embedded within a single product, it becomes more important to accurately identify the customers' needs in order to distribute performance in a product. Various studies have attempted to understand customers' needs related to product developments. The methods used include face-to-face surveys that directly ask customers' opinions, non-face-to-face surveys, and indirect customer demand verification through comparative evaluations of competing products. There are pros and cons to each of these methods. In the case of face-to-face surveys, the disadvantage is that they are costly and time consuming. These shortcomings make them difficult to perform repeatedly and frequently. In addition, there is concern about bias when selecting a survey subject that is not representative, because of the small number of samples. One advantage is being able to understand customer opinions in detail. Conversely, in the case of online surveys, they are more cost-effective and time-efficient compared to face-to-face surveys, but only responses to the survey questionnaire can be identified, which can lead to significant \begin{table}
\begin{tabular}{c c c c c} \hline  & **Planning** & **Concept Design** & **Design** & **Test** \\ \hline MKTG 1 & Market analysis & Collect user voice & Set MKTG plan & Enhance field test \\ Design & Structure study & Concept study & Structure design & \\ Technology study & Prototyping & (shape/material) & Check performance \\ MFG 2 & Supply chain build & Set MFG cost & Tool design & Set assemble plan \\ Check restriction & & Define MFG process & Start supply \\ \hline \end{tabular}  
* MKTG: marketing; 2 MFG: manufacturing.  
\end{table} 
Table 1: Product development process. Figure 2: Areas of product development process. differences in results depending on the survey design, and it is difficult to identify causal relationships. A number of studies have confirmed that the two methods are somewhat lacking in reliability or depth of investigation, as participation is often due to compensation rather than voluntary participation by customers [8; 9]. Recently, there have been studies using online reviews from customers to overcome the limitations of the other survey methods. Online reviews are sentences or paragraphs that users formulate to post their opinions about the product after using it on the Internet, which can be collected from a community, forum, or blog. Online reviews have an efficiency and reliability advantage compared to the aforementioned methods [10]. First, they have an edge in terms of the reliability of the reviews because they are based on voluntary participation. In addition, when research methodologies related to big data and natural language processing are introduced, the risk of bias and reliability is reduced by using overwhelmingly more samples than other types of surveys [11]. Based on natural language processing techniques and big data, [PERSON] and [PERSON] used these advantages to examine users' use environment through customer reviews [12] and, in other studies, they extracted consumers' choice sets based on reviews [13]. In addition, [PERSON] and [PERSON] classified topics in reviews and conducted an analysis to quantitatively extract consumers' emotional evaluations of product reviews [14]. For basic online review analysis, the process is carried out in the following order: collection-preprocessing-analysis. An overview is shown in Figure 3. This involves collecting a number of reviews and doing preprocessing work, such as deleting unused words and dismantling sentences from reviews.