  The digital transformation of companies has led to the evolution of databases
towards Big Data. Our work is part of this context and concerns more
particularly the mechanisms to extract datasets stored in a Data Lake and to
store the data in a Data Warehouse. The latter will allow, in a second time,
decisional analysis. In this paper, we present the extraction mechanism limited
to relational databases. To automate this process, we used the Model Driven
Architecture (MDA), which offers a formalized environment for schema
transformation. From the physical schemas describing a Data Lake, we propose
transformation rules that allow the creation of a Data Warehouse stored on a
document-oriented NoSQL system. An experimentation of the transformation
process has been performed on a medical application.
