  In this work we will consider the concepts of partial and complete
observables for canonical general relativity. These concepts provide a method
to calculate Dirac observables. The central result of this work is that one can
compute Dirac observables for general relativity by dealing with just one
constraint. For this we have to introduce spatial diffeomorphism invariant
Hamiltonian constraints. It will turn out that these can be made to be Abelian.
Furthermore the methods outlined here provide a connection between observables
in the space--time picture, i.e. quantities invariant under space--time
diffeomorphisms, and Dirac observables in the canonical picture.
