We propose to demonstrate a system for accessing Key-Value stores in the presence of semantic constraints, as considered in the setting of ontology-mediated query answering. The constraints we study are expressed in a native rule language for JSON records and their purpose is to establish a high level view over a collection of legacy and possibly heterogenous Key-Value stores. To ensure correct and complete data access, constraints are taken into account via query rewriting techniques tailored for MongoDB queries. The nature of queries and constraints also enable the deployment of parallelization techniques for optimizing query rewriting and therefore the whole data access task. During the demonstration, attendees will first be able to query JSON datasets in the presence of rules thereby illustrating how semantic constraints bring novel and pertinent answers to queries. Then, it will be possible to make a detailed analysis of query rewriting and compare the parallel version of the reformulation algorithm with the baseline centralized one.