  We suggest a general formalism to treat a baryon as a composite system of
three quarks and a `sea'. In this formalism, the sea is a cluster which can
consists of gluons and quark-antiquark pairs. The hadron wave function with a
sea component is given. The magnetic moments, related sum rules and axial weak
coupling constants are obtained. The data seems to favor a vector sea rather
than a scalar sea. The quark spin distributions in the nucleon are also
discussed.
