  The problem of maximizing information diffusion, given a certain budget
expressed in terms of the number of seed nodes, is an important topic in social
networks research. Existing literature focuses on single phase diffusion where
all seed nodes are selected at the beginning of diffusion and all the selected
nodes are activated simultaneously. This paper undertakes a detailed
investigation of the effect of selecting and activating seed nodes in multiple
phases. Specifically, we study diffusion in two phases assuming the
well-studied independent cascade model. First, we formulate an objective
function for two-phase diffusion, investigate its properties, and propose
efficient algorithms for finding seed nodes in the two phases. Next, we study
two associated problems: (1) budget splitting which seeks to optimally split
the total budget between the two phases and (2) scheduling which seeks to
determine an optimal delay after which to commence the second phase. Our main
conclusions include: (a) under strict temporal constraints, use single phase
diffusion, (b) under moderate temporal constraints, use two-phase diffusion
with a short delay while allocating most of the budget to the first phase, and
(c) when there are no temporal constraints, use two-phase diffusion with a long
delay while allocating roughly one-third of the budget to the first phase.
