BigDataFr recommends: Data modeling with multi-model databases
A case study for mixing different data models within the same data store.

‘In recent years, the idea of “polyglot persistence” has emerged and become popular — for example, see Martin Fowler’s excellent blog post. Fowler’s basic idea can be interpreted that it is beneficial to use a variety of appropriate data models for different parts of the persistence layer of larger software architectures.

According to this, one would, for example, use a relational database to persist structured, tabular data; a document store for unstructured, object-like data; a key/value store for a hash table; and a graph database for highly linked referential data.’

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By Max Neunhöffer
Source: radar.oreilly.com