Over the years, robot-aided therapy has been introduced to the field of physiotherapy for stroke or spinal cord injury as a new approach. It has shown that the robots have strong potential in dealing with therapeutic applications. However, rehabilitation robots for clinical environment have not been fully utilized in everyday therapy activities due to concerns over the lack of usability, which is usually identified as the problems of safety and user-friendliness. From the viewpoint of software engineering, a user-centred design process based on UML (Unified Modelling Language) has been known to be a best solution to satisfy usability since the design process relies highly on the analysis of users and their tasks to reach their goals. Therefore, a modelling method using UML is applied to the development of computer-based interaction and rehabilitation information system for rehabilitation robotics. A survey was conducted in order to determine the requirements of physiotherapists. A new graphical notation for interactive elements and their connection methods was proposed to overcome the shortage of existing UML notations. This model-driven approach to the interactive system using UML supported by the new interaction models is expected to produce a therapy robot that satisfies physiotherapists.