# 13.2.3 DataLink protocol for lightcurves / epoch photometry

Different Gaia data releases provide additional information for the catalogue sources. Apart from the five-parameter astrometric solution, other data sets like lightcurves, spectroscopic data, and variable-star classifications will be added in connection with the main Gaia catalogue. The richness and complexity of the Gaia data increases for each new release. Ensuring a reasonable data access performance as the volume grows poses a significant technical challenge.

The Gaia Archive deployed for Gaia DR2 offers the first implementation of a flexible IVOA protocol called DataLink. This protocol allows the discovery of extra metadata associated to a certain row (that is, an astronomical source) by the publication of a RESTful protocol that includes links to different kinds of data, including for instance time series, spectral data, or calibration files.

For Gaia DR2, the DataLink service provides access to photometric time series (lightcurves) of $\sim$$550\,000$ selected, variable objects. The Archive online help https://www.cosmos.esa.int/web/gaia-users/archive/help provides both a detailed description of the interfaces (see ’Datalink service’ section) and a hands-on tutorial on how to work with Gaia DR2 lightcurves (see ’Tutorials - Datalink and light curves’ section).