A survey on chatbot systems from rule-based models to system-integrated natural user interfaces

Chatbot systems have evolved from rule-based conversational tools to advanced data-driven systems that support more complex interaction. This paper examines this evolution and examines how advanced chatbot systems may function as System-Integrated Conversational Natural User Interfaces (System-Integrated Conversational NUIs). In this role, natural-language interaction serves as a user-facing interface to broader digital capabilities rather than only supporting conversational response generation. The paper provides a structured review of key stages in chatbot development, introduces the System-Integrated Conversational NUI as an interface-centred concept, and proposes a conceptual architecture and design principles for this expanded interface role. Key challenges and future considerations are also discussed, with particular attention to interaction quality, system complexity, responsible operation, and the coexistence of conversational and structured interface elements. This study provides a conceptual basis for analysing and designing advanced chatbot systems that support natural-language access to connected digital capabilities.