  We give a unitary irreducible representation of the proper Poincar\'e group
that leads to an operational version of the classical relativistic dynamics of
a massive spinless particle. Unlike quantum mechanics, in this operational
theory there is no uncertainty principle between position and momentum. It will
be shown that the theory contains the Koopman-von Neumann formalism as a
particular case, and a explicit connection with relativistic Hamiltonian
mechanics will be given.
