Four dimensional N=2 generalized superconformal field theory can be defined
by compactifying six dimensional (0,2) theory on a Riemann surface with regular
punctures. In previous studies, gauge coupling constant space is identified
with the moduli space of punctured Riemann surface M_{g,n}. We show that the
weakly coupled gauge group description corresponds to a stable nodal curve, and
the coupling space is actually the Deligne-Mumford compactification
\bar{M}_{g,n}. We also give an algorithm to determine the weakly coupled gauge
group and matter content in any duality frame.Comment: v2, reorganizing the materials, discussions on 2d CFT is remove
