Editing X-machine (section)

The '''X-machine''' (''XM'') is a theoretical model of [[computation]] introduced by [[Samuel Eilenberg]] in 1974.<ref
  name="Eil74">S. Eilenberg (1974)
  ''Automata, Languages and Machines, Vol. A''. 
  Academic Press, London.</ref>
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 [[Relation (mathematics)|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.