Towards a Standard for JSON Document Databases

In this technical report, we present a formalisation of the MongoDB aggregation framework. Our aim is to identify a fragment that could serve as the starting point for an industry-wide standard for querying JSON document databases. We provide a syntax and formal semantics for a set of selected operators, We show how this fragment relates to known relational query languages. We explain how our semantics differs from the current implementation of MongoDB, and justify our choices. We provide a set of algebraic transformations that can be used for query optimisation.