In dynamic epistemic logic (Van Ditmarsch et al., 2008) it is customary to
use an action frame (Baltag and Moss, 2004; Baltag et al., 1998) to describe
different views of a single action. In this article, action frames are extended
to add or remove agents, we call these agent-update frames. This can be done
selectively so that only some specified agents get information of the update,
which can be used to model several interesting examples such as private update
and deception, studied earlier by Baltag and Moss (2004); Sakama (2015); Van
Ditmarsch et al. (2012). The product update of a Kripke model by an action
frame is an abbreviated way of describing the transformed Kripke model which is
the result of performing the action. This is substantially extended to a
sum-product update of a Kripke model by an agent-update frame in the new
setting. These ideas are applied to an AI problem of modelling a story. We show
that dynamic epistemic logics, with update modalities now based on agent-update
frames, continue to have sound and complete proof systems. Decision procedures
for model checking and satisfiability have expected complexity. A sublanguage
is shown to have polynomial space algorithms