  Dalitz decays of a hyperon resonance to a ground-state hyperon and an
electron-positron pair can give access to some information about the composite
structure of hyperons. We present expressions for the multi-differential decay
rates in terms of general transition form factors for spin-parity combinations
J^P = 1/2^+/-, 3/2^+/- of the hyperon resonance. Even if the spin of the
initial hyperon resonance is not measured, the self-analyzing weak decay of the
"final" ground-state hyperon contains information about the relative phase
between combinations of transition form factors. This relative phase is
non-vanishing because of the unstable nature of the hyperon resonance. If all
form factor combinations in the differential decay formulae are replaced by
their respective values at the photon point, one obtains a QED type
approximation, which might be interpreted as characterizing hypothetical
hyperons with point-like structure. We compare the QED type approximation to a
more realistic form factor scenario for the lowest-lying singly-strange hyperon
resonances. In this way we explore which accuracy in the measurements of the
differential Dalitz decay rates is required in order to distinguish the
composite-structure case from the pointlike case. Based on the QED type
approximation we obtain as a by-product a rough prediction for the ratio
between the Dalitz decay width and the corresponding photon decay width.
