The analysis of relational and NoSQL databases leads to the conclusion that these data processing systems are to some extent complementary. In current Big Data applications, especially where extensive analyses are needed, it turns out that it is non-trivial to design an infrastructure involving software of both types.
In terms of performance, it may even be beneficial to transform the SQL database schema into NoSQL or to perform double-sided data migration between relational and NoSQL databases. The aim of the article is to discuss these possibilities and some new meth-ods of designing such database architectures standing on the legacy of the three-level ANSI/SPARC architecture.