  We obtain an approximate global stationary and axisymmetric solution of
Einstein's equations which can be thought as a simple star model: a
self-gravitating perfect fluid ball with a differential rotation motion
pattern. Using the post--Minkowskian formalism (weak field approximation) and
considering rotation as a perturbation (slow rotation approximation), we find
approximate interior and exterior (asymptotically flat) solutions to this
problem in harmonic coordinates. Interior and exterior solutions are matched,
in the sense of Lichnerowicz, on the surface of zero pressure to get a global
solution. The resulting metric depends on four arbitrary constants: mass
density, rotational velocity at $r=0$, a parameter which takes into account of
the change in the rotational velocity through the star and the star radius in
the non-rotation limit. The mass, angular momentum, quadrupole moment and other
constants of the exterior metric are determined in terms of these four
parameters.
