  The vast amounts of data to be collected by the Giant Radio Array for
Neutrino Detection (GRAND) and its prototype - GRANDProto300 - require the use
of a data format very efficient in terms of i/o speed and compression. At the
same time, the data should be easily accessible, without the knowledge of the
intricacies of the format, both for bulk processing and for detailed
event-by-event analysis and reconstruction. We present the format and the
structure prepared for GRAND data, the concept of the data-processing chain,
and data-oriented and analysis-oriented interfaces written in Python.
