Abstract
The next generation experiments in High Energy Physics are the driving force for setting up an International Data Grid at CERN, the European Organization for Nuclear Research. Hundreds of Petabytes of data will be distributed and replicated all over the globe starting from 2005. In order to analyse this massive set of distributed data efficiently, we propose a hierarchical query optimisation architecture based on multi-agent technology. The architecture is optimised for the High Energy Physics community but is representative also for other data intensive scientific applications that use distributed data stores and mass storage systems.