We discuss our recently proposed
model-independent framework for fitting hadronic form-factor data, which are
often only available at discrete kinematical points, using parameterisations
based on unitarity and analyticity. The accompanying dispersive bound on the
form factors (unitarity constraint) is used to regulate the ill-posed fitting
problem and allow model-independent predictions over the entire physical
range. Kinematical constraints, for example for the vector and scalar form
factors in semileptonic meson decays, can be imposed exactly. The core
formulae are straight-forward to implement with standard math libraries. We
demonstrate the method for the exclusive semileptonic decay $B_s\to K\ell\nu$,
an example requiring one to use a generalisation of the original
Boyd Grinstein Lebed (BGL) unitarity constraint. We further present a first
application of the method to $B \to D^*\ell \nu$ decays.