  New special types of stationary conservative impedance and scattering
systems, the so-called non-canonical systems, involving triplets of Hilbert
spaces and projection operators, are considered. It is established that every
matrix-valued Herglotz-Nevanlinna function of the form
V(z)=Q+Lz+\int_{\dR}(\frac{1}{t-z}-\frac{t}{1+t^2})d\Sigma(t) can be realized
as a transfer function of such a new type of conservative impedance system. In
this case it is shown that the realization can be chosen such that the main and
the projection operators of the realizing system satisfy a certain
commutativity condition if and only if L=0. It is also shown that $V(z)$ with
an additional condition (namely, $L$ is invertible or L=0), can be realized as
a linear fractional transformation of the transfer function of a non-canonical
scattering $F_+$-system. In particular, this means that every scalar
Herglotz-Nevanlinna function can be realized in the above sense.
  Moreover, the classical Livsic systems (Brodskii-Livsic operator
colligations) can be derived from $F_+$-systems as a special case when $F_+=I$
and the spectral measure $d\Sigma(t)$ is compactly supported. The realization
theorems proved in this paper are strongly connected with, and complement the
recent results by Ball and Staffans.
