The start_chat.launch launch file launches the aiml_server and aiml_client nodes. Before running this launch file, you have to set the data folder path that is set as the ROS parameter. You can set it as your AIML data folder path:

    <launch> 
      <param name="aiml_path" 
    value="/home/robot/ros_robotics_projects_ws/src/ros_aiml/data" /> 
      <node name="aiml_server" pkg="ros_aiml" type="aiml_server.py" 
    output="screen"> 
      </node> 
      <node name="aiml_client" pkg="ros_aiml" type="aiml_client.py" 
    output="screen"> 
      </node> 
    </launch>