I. Introduction
Owing to the development of technology and the internet infrastructure, methods of information dissemination in a variety of forms are increasing, such as text, audio, video, virtual reality, and mixed media in personal cyberspace, public social groups, communication applications, and so on. Moreover, mobile devices are widely used, such as smartphones, tablets, and notebooks that connect with or communicate with the internet. Therefore, information is distributed and obtained more rapidly than before. Many services have transformed from offline to online services, such as customer service, reservations, shopping, and so on.