This chapter was entirely dedicated to non-relational databases. At the very beginning, we introduced you to the general concept of highly-scalable, NoSQL databases with flexible schemas. We have discussed their major features and presented practical applications in which they excel when compared with standard relational SQL databases.
We then began a series of tutorials that were aimed at explaining how to read, manage, process, and query data stored in a very popular, open source NoSQL database called MongoDB. We reviewed three leading R packages that allow users to implement a variety of techniques and methods in MongoDB directly from the R environment.
Finally, we introduced you to an open source, non-relational and distributed HBase database that operates on top of the Hadoop Distributed File System. We guided you through some time-consuming installation procedures to enable you to connect to HBase using R. We then showed you several examples of how to apply functions in the