High Quality Content by WIKIPEDIA articles! The X-machine (XM) is a theoretical model of computation introduced by Samuel Eilenberg in 1974. THe X in "X-machine" represents the fundamental data type on which the machine operates; for example, a machine that operates on databases (objects of type database) would be a database-machine. THe X-machine model is structurally the same as the finite state machine, except that the symbols used to label the machine's transitions denote relations of type X X. CRossing a transition is equivalent to applying the relation that labels it (computing a set of changes to the data type X), and traversing a path in the machine corresponds to applying all the associated relations, one after the other.