13.1 Introduction

The ESDC (Arviset (2015)) (ESAC Science Data Centre), located at ESAC, is responsible for the design and implementation of ESA’s space science missions (astronomy, planetary science and heliophysics) archives. This group is also responsible for the long-term preservation of the data. In particular, ESDC is responsible of the implementation and maintenance of the ESA Gaia archive.

This archive has designed to allow an easy access and exploitation of the Gaia products and, also, as a central repository to enable the validation of the catalogue before the public release and, also, for distribution of the Gaia products to other data centres.

Due to the size and complexity of the Gaia products, the ESA Gaia archive has been designed following the approach ”bring code to the data”. For the Gaia DR1 and Gaia DR2, which the main product is a catalogue, the approach followed has been the extension of the IVOA protocol TAP (Tabular Access Protocol). TAP provides a remote database invocation using a language similar to SQL called ADQL. ADQL, another standard from the IVOA, is a subset of SQL that incorporates some geometrical functions (like CIRCLE, DISTANCE, OVERLAPS, CONTAINS, etc.) that simplify the typical queries done by scientists when they explore big catalogues.

However, standard TAP does not provide clear rules on how to handle proprietary data, how to share data or user tables, what are requirements for the Gaia archive, and this is why ESDC developed the concept of TAP+, a backwards compatible extension of TAP that fulfils the needs of the Gaia mission.

TAP+ is an extension of the standard IVOA TAP that, in some ways, has the popular service CasJobs, from MAST/STScI, as a precursor. Similar to this service, two different execution queues (synchronous and asynchronous) are defined, users have their own database schemas with persistent areas and there are quotes and maximum execution times for the queries. The main differences are that TAP+ maintains compatibility with standard IVOA protocols, it has been defined using REST protocols (instead of SOAP) and it also uses standard query languages (like ADQL). As a result, the Gaia Archive can be queried by most of the VO-compatible applications and users can interact with the archive in a more standard way.

More information on the Gaia archive and TAP+, can be found at (Salgado et al. (2017))