An voice command processing method provides a unified voice control interface to access and control Internet of things (IoT) devices and configure value of attributes of graphical user interface (GUI) elements, attributes of applications, and attributes of the IoT devices. As a voice command comprises an expression of a percentage or a fraction of a baseline value of an attribute, or an exact value of the attribute of an IoT device, the unified voice control interface sets the attribute of the IoT device in response to the percentage, the fraction, or the exact value in the voice command.