The DataTiles system integrates the benefits of two major interaction paradigms: graphical and physical user interfaces. Tagged transparent tiles are used as modular construction units. These tiles are augmented by dynamic graphical information when they are placed on a sensor-enhanced flat panel display. They can be used independently or can be combined into more complex configurations, similar to the way language can express complex concepts through a sequence of simple words. In this paper, we discuss our design principles for mixing physical and graphical interface techniques, and describe the system architecture and example applications of the DataTiles system. Keywords Interaction techniques, tangible user interfaces, graphical user interfaces, visual language, radio-frequency identification tags