  During more than 17 years of operation in space INTEGRAL telescope has
accumulated large data set that contains records of hard X-ray and soft
gamma-ray astronomical sources. These data can be re-used in the context of
multi-wavelength or multi-messenger studies of astronomical sources and have to
be preserved on long time scales. We present a scientific validation of an
interactive online INTEGRAL data analysis system for multi-wavelength studies
of hard X-ray and soft gamma-ray sources. The online data analysis system
generates publication-quality high-level data products: sky images, spectra and
light-curves in response to user queries that define analysis parameters, such
as source position, time and energy interval and binning. The data products can
be requested via a web browser interface or via Application Programming
Interface (API) available as a Python package. The analysis workflow organized
to preserve and re-use various intermediate analysis products, ensuring that
frequently requested results are available without delay. The platform can be
deployed in any compatible infrastructure. We report the functionalities and
performance of the online data analysis system by reproducing the benchmark
INTEGRAL results on different types of sources, including bright steady and
transient Galactic sources, and bright and weak variable extra-galactic
sources. We compare the results obtained with the online data analysis system
with previously published results on these sources. We consider the INTEGRAL
online data analysis as a demonstrator of more general web-based "data analysis
as a service" approach that provides a promising solution for preservation and
maintenance of data analysis tools of astronomical telescopes on (multi)decade
long time scales and facilitates combination of data in multi-wavelength and
multi-messenger studies of astronomical sources.
