  More than half a million of the 1.69 billion sources in Gaia Data Release 2
(DR2) are published with photometric time series that exhibit light variations
during the 22 months of observation. An all-sky classification of common
high-amplitude pulsators (Cepheids, long-period variables, Delta Scuti / SX
Phoenicis, and RR Lyrae stars) is provided for stars with brightness variations
greater than 0.1 mag in G band. A semi-supervised classification approach was
employed, firstly training multi-stage random forest classifiers with sources
of known types in the literature, followed by a preliminary classification of
the Gaia data and a second training phase that included a selection of the
first classification results to improve the representation of some classes,
before the improved classifiers were applied to the Gaia data. Dedicated
validation classifiers were used to reduce the level of contamination in the
published results. A relevant fraction of objects were not yet sufficiently
sampled for reliable Fourier series decomposition, consequently classifiers
were based on features derived from statistics of photometric time series in
the G, BP, and RP bands, as well as from some astrometric parameters. The
published classification results include 195,780 RR Lyrae stars, 150,757
long-period variables, 8550 Cepheids, and 8882 Delta Scuti / SX Phoenicis
stars. All of these results represent candidates whose completeness and
contamination are described as a function of variability type and
classification reliability. Results are expressed in terms of class labels and
classification scores, which are available in the vari_classifier_result table
of the Gaia archive.
