AMGA is a generic metadata catalogue that is intended to provide access to relational data for a wide range of applications. The main features of the AMGA catalogue are high performance access to relational databases, especially on WAN connections. An SQL-like query language providing most of the features of modern SQL dialects provides complex joins and includes string and mathematical functions. This query language serves to hide the differences of various vendor dialects of SQL and is translated into the correct dialect of the back-end. In addition this query language allows to implement a fine grained access control, which is based on the built-in support for user and group management. VOMS groups and roles are supported.