The LXS DBMS is a polystore database that provides access to different and heterogeneous datastores via a common interface. It allows for the data user to submit a query, whose scan operators can request data that are stored in external datastores, and combine their intermediate results with data coming from other sources, either LXS internal datastore or others. For instance, a JOIN operator might require to JOIN table A (resigned in LXS) and table B (resigned in a MongoDB or a Hadoop DataLake). At this phase, there is a support for a limited target datastores, for Proof-of-Concept of the prototype. Moreover, the user has to write queries for the target datastores in the specific dialect. What is more, JOIN operations are not efficient, as they require all data resigned in an external datastore to be retrieved in the query engine level.