FAIRsharing record for: Astronomical Data Query Language

This FAIRsharing record describes: The Astronomical Data Query Language (ADQL) is the language used by the IVOA to represent astronomy queries posted to VO services. The IVOA has developed several standardized protocols to access astronomical data, e.g., Simple Image Access (SIA) protocol and Simple Spectral Access (SSA) protocol for image and spectral data respectively. These protocols might be satisfied using a single table query. However, different VO services have different needs in terms of query complexity and ADQL arises in this context. The ADQL specification makes no distinction between core and advanced or extended functionalities. Hence ADQL has been built according to a single Backus Naur Form (BNF) based language definition. Any service making use of ADQL would then define the level of compliancy to the language. This would allow the notion of core and extension to be service-driven and it would decouple the language from the service specifications. ADQL is based on the Structured Query Language (SQL), especially on SQL 92 1 2 3. . The VO has a number of tabular data sets and many of them are stored in relational databases, making SQL a convenient access means. A subset of the SQL grammar has been extended to support queries that are specific to astronomy. Similarly to SQL, the ADQL language definition is not semantically safe by design and therefore this specification defines syntactical correctness only. Type safety has been achieved as far as it can be done in SQL.