  We consider an operator-theoretic approach to linear infinite-dimensional
port-Hamiltonian systems. In particular, we use the theory of system nodes by
Staffans to formulate a~suitable concept for port-Hamiltonian systems, which
allows a unifying approach to systems with boundary as well as distributed
control and observation. The concept presented in this article is further
neither limited to parabolic nor hyperbolic systems, and it also covers partial
differential equations on multi-dimensional spatial domains. Our presented
theory is substantiated by means of several physical examples.
