The diffractlve exc~tation model (DEM) is formulated in terms of rapidity, and used to calculate the inclusive rapidity distributions p p -. .rr X and p p .rr n-X . tising simplified kinematics, analytic calculations are made for these distributions and the related multiplicity moments. The two-pion correlations in the isotropic-decay model are found to be in agreement with experiment at low energies, but rise too rapidly with energy, lying an order of magnitude abote Intersecting-Storage-Rings data. A modified DEM, with longitudinal decay of the diffractwe cluster, accounts for the size and weak energy dependence of correlations in the diffractive part of the inelastic cross section. This model is found suitable for use as the diffractive component in a two-component model.