  Service-oriented wireless sensor network(WSN) has been recently proposed as
an architecture to rapidly develop applications in WSNs. In WSNs, a query task
may require a set of services and may be carried out repetitively with a given
frequency during its lifetime. A service composition solution shall be provided
for each execution of such a persistent query task. Due to the energy saving
strategy, some sensors may be scheduled to be in sleep mode periodically. Thus,
a service composition solution may not always be valid during the lifetime of a
persistent query. When a query task needs to be conducted over a new service
composition solution, a routing update procedure is involved which consumes
energy. In this paper, we study service composition design which minimizes the
number of service composition solutions during the lifetime of a persistent
query. We also aim to minimize the total service composition cost when the
minimum number of required service composition solutions is derived. A greedy
algorithm and a dynamic programming algorithm are proposed to complete these
two objectives respectively. The optimality of both algorithms provides the
service composition solutions for a persistent query with minimum energy
consumption.
