  In modern application areas for software systems --- like eHealth, the
Internet-of-Things, and Edge Computing --- data is encoded in heterogeneous,
tree-shaped data-formats, it must be processed in real-time, and it must be
ephemeral, i.e., not persist in the system. While it is preferable to use a
query language to express complex data-handling logic, their typical execution
engine, a database external from the main application, is unfit in scenarios of
ephemeral data-handling. A better option is represented by integrated query
frameworks, which benefit from existing development support tools (e.g., syntax
and type checkers) and execute within the application memory. In this paper, we
propose one such framework that, for the first time, targets tree-shaped,
document-oriented queries. We formalise an instantiation of MQuery, a sound
variant of the widely-used MongoDB query language, which we implemented in the
Jolie language. Jolie programs are microservices, the building blocks of modern
software systems. Moreover, since Jolie supports native tree data-structures
and automatic management of heterogeneous data-encodings, we can provide a
uniform way to use MQuery on any data-format supported by the language. We
present a non-trivial use case from eHealth, use it to concretely evaluate our
model, and to illustrate our formalism.
