"...tangible computing has been explored, largely, as a practical exercise. Most prototypes have been developed opportunistically, driven as much by the availability of sensor technology and the emergence of new control devices as by a reasoned understanding of the role of physicality in interaction. We have various clues and pointers, but there is no theory of tangible interaction." (Dourish, P. "Where the action is" [p.52](http://books.google.com/books?id=DCIy2zxrCqcC&lpg=PA52&ots=oC2792a5Sg&dq=at%20the%20same%20time%20tangible%20computing%20has%20been%20explored%20largely%20as%20a%20practical%20exercise&pg=PA52#v=onepage&q&f=false))