Design principles of the Metadata Querying Language (MQL) implemented in the ATLAS Metadata Interface (AMI) ecosystem

ATLAS Metadata Interface (AMI) is a generic ecosystem for metadata aggregation, transformation and cataloging benefiting from about 20 years of feedback in the LHC context. This poster describes the design principles of the Metadata Querying Language (MQL) implemented in AMI, a metadata-oriented domain-specific language allowing to query databases without knowing the relation between tables. With this simplified yet generic grammar, MQL permits writing complex queries much more simply than Structured Query Language (SQL). The poster describes how AMI compiles MQL into SQL queries using the underlying table relations graph automatically extracted through a reflexion mechanism