  We provide decompositions of Dirichlet forms into recurrent and transient
parts as well as into conservative and dissipative parts, in the framework of
Hausdorff state spaces. Combining both formulae we write every Dirichlet form
as the sum of a recurrent, dissipative and transient conservative Dirichlet
forms. Besides, we prove that Mosco convergence preserves invariant sets and
that a Dirichlet form shares the same invariants sets with its approximating
Dirichlet forms E(t) and E(?). Finally we show the equivalence between
conservativeness (resp. dissipativity) of a Dirichlet form and the
conservativeness (reps. dissipativity) of E(t) and E(?). The elaborated results
are enlightened by some examples.
