3.1. Dialogue System

Dialogue systems, conversational agents or chatbots are software programs that support conversational interaction between humans and machines in natural language [10]. It can be based on text-based or speech-based and can also be used on different devices. Typically, dialogue systems can classify into two categories—a task-oriented dialogue system which is used in this paper; and a non-task-oriented dialogue system or chatbot. The task-oriented dialogue system is designed for a particular task and set up to have short conversations [19,20] such as booking flight tickets, talking to customer care service and asking about the weather. While a non-task-oriented dialogue system or chatbot is designed for unstructured conversational as a conversation between human and human [21,22]. The dialogue system requires an understanding of natural language in order to process user queries.