  German-Russian Astroparticle Data Life Cycle Initiative is an international
project whose aim is to develop a distributed data storage system that
aggregates data from the storage systems of different astroparticle
experiments. The prototype of such a system, which is called the Astroparticle
Physics Distributed Data Storage (APPDS), has been being developed. In this
paper, the Data Aggregation Service, one of the core services of APDDS, is
presented. The Data Aggregation Service connects all distributed services of
APPDS together to find the necessary data and deliver them to users on demand.
