## 7 Conclusions and Future Work  
With the rapid expansion of internet innovations, SNS have become a useful source for gathering customer opinions. Taking advantage of this big opportunity, software requirements engineers have started considering SNS to elicit user requirements in order to evolve the SPL products quickly. Users' opinion is essential for SPL organizations to better understand the general responses of end-users to their products and improve their products with the passage of time. In addition, users' opinion enables SPL organizations to figure out the specific needs of individual users that can facilitate subsequent SPL strategies to meet the specified needs of the individual user. This paper presented an SNS-based RE process to elicit user requirements from SNS considering SPL systems. The key superiority of this article is that it is considering VR and CR while other research is focused on gathering requirements and stakeholder prioritization. We have proposed a model to determine VR and CR by considering the attributes of user opinion which is a distention of this research. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **SNS** & **Moderator** & \
\begin{tabular}{c} **Requirements** \\ **Elicitation** \\ \end{tabular} &
\begin{tabular}{c} **VR and CR** \\ **Analysis** \\ \end{tabular} \\ \hline
[45] & \(\bullet\) & \(\circ\) & \(\bullet\) & \(\circ\) \\
[15] & \(\bullet\) & \(\circ\) & \(\bullet\) & \(\circ\) \\
[14] & \(\bullet\) & \(\circ\) & \(\bullet\) & \(\circ\) \\
[13] & \(\bullet\) & \(\circ\) & \(\bullet\) & \(\circ\) \\
[48] & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\circ\) \\
[54] & \(\bullet\) & \(\circ\) & \(\bullet\) & \(\circ\) \\
[55] & \(\bullet\) & \(\circ\) & \(\bullet\) & \(\circ\) \\ \hline \hline \end{tabular} SNS: Social Network Services, VR: Variable Requirements, CR: Common Requirements.  
\end{table} 
Table 13: _Cont_. The applicability of the SNS-based RE process for elicitation of requirements to evolve SPL products is shown through a controlled experiment performed by using Facebook and Twitter. The participants in the experiment were grouped into teams each consisting of 15 members with various roles. The task was to elicit user requirements for the smartwatch domain. One team conducted the task by using the SNS-based RE process conjoining with Twitter and Facebook and the other group executed the task with the traditional RE process, i.e., by interview and online surveys. We gathered the data from both teams and performed tests on the provided data to know the efficiency and effectiveness of the SNS-based RE process. The results from the experiment show that the proposed SNS-based RE process effectively and efficiently elicits user requirements considering VR and CR. As mentioned above, our proposed approach has two parts: (1) identifying requirements using SNS and (2) classifying requirements into variable requirements and common requirements using Equation (1). If we consider VR and CR as general plain requirements, then our approach can be used as a general approach to elicit users' requirements from SNS. Our approach can also be used in reused-based software development which can expedite the time to market, reduce laborious work and improve productivity and quality. This research has limitations which will be addressed in future work. There are moderator roles and domain expert roles who are in fact human beings. There is a chance of human error in interpreting the extracted keywords into requirements. Therefore, automatic tools should be developed with the help of NLP to process the users' opinion. Eventually, this will enable us to minimize the role of moderators and domain experts. The extended studies connected with our research can consider a technique to dynamically map between elicited requirements to the components of domain architecture. Conceptualization, N.A. and J.-E.H.; Methodology, N.A. ; Validation, J.-E.H.; Statistical Analysis, N.A. ; Data Collection, N.A. ; Writing--Original Draft Preparation, N.A.