  The Chew-Mandelstam parameterization, which has been used extensively in the
two-body hadronic sector, is generalized in this exploratory study to the
electromagnetic sector by simultaneous fits to the pion- and
eta-photoproduction S-wave multipole amplitudes for center-of-mass energies
from the pion threshold through 1.61 GeV. We review the Chew-Mandelstam
parameterization in detail to clarify the theoretical content of the SAID
hadronic amplitude analysis and to place the proposed, generalized SAID
electromagnetic amplitudes in the context of earlier employed parameterized
forms. The parameterization is unitary at the two-body level, employing four
hadronic channels and the gamma-N electromagnetic channel. We compare the
resulting fit to the MAID parameterization and find qualitative agreement
though, numerically, the solution is somewhat different. Applications of the
extended parameterization to global fits of the photoproduction data and to
global fits of the combined hadronic and photoproduction data are discussed.
