A flexible and modular data format ROOT-based implementation for HEP

Data access and availability is a crucial issue in high energy physics (HEP) experiments, given the huge amount of data produced. We present a flexible and modular data format implementation for HEP applications. It has been designed to modularize data in order to update the minimum amount of event information in case of bug correction, software updates or data format extension, to simplify data distribution and upgrades to the regional data centers, and to reduce the amount of data to be transferred to data members really affected by reprocessing. The proposed design and implementation has been developed as mini-DST data format for the Alpha Magnetic Spectrometer (AMS [1]) experiment on the International Space Station (ISS) and is based on the CERN ROOT [2] toolkit.