  To each del Pezzo surface (resp. ruled surface, ruled surface with a
section), we describe a natural Lie algebra bundle of type E_n (resp. D_n, A_n)
over it. Using lines and rulings on any such surface, we describe various
representation bundles corresponding to fundamental representations of the
corresponding Lie algebra.
  When we specify a geometric structure on the surface to reduce the Lie
algebra to a smaller one, then the classical geometry of the configuration of
lines and rulings is encoded beautifully by the branching rules in Lie theory.
We discuss this relationship in details.
  When we degenerate the surface to a non-normal del Pezzo surface, we discover
that the configurations of lines and rulings are also governed by certain
branching rules.
