  The Semimicroscopic Algebraic Cluster Model (SACM) is applied to 12C as a
system of three alpha- clusters. The microscopic model space, which observes
the Pauli-Exclusion-Principle (PEP), is constructed. It is shown that the 12C
nucleus can effectively be treated as a two-cluster system 8Be+alpha. The
experimental spectrum is well reproduced. The geometrical mapping is discussed
and it is shown that the ground state must correspond to a triangular
structure, which is in agreement with other microscopic calculations. The
non-zero B(E2; 0_2+ --> 2_1+) transition requires a mixing of SU(3) irreducible
representations (irreps) whose consequences are discussed. The Hoyle state
turns out to contain large shell excitations. The results are compared to
another phenomenological model, which assumes a triangular structure and, using
simple symmetry arguments, can reproduce the states observed at low energy.
This model does not observe the PEP and one objective of our contribution is to
verify the extend of importance of the PEP.
