E. F. Codd proposed three normal forms: 1NF, 2NF and 3NF (1970). A revised definition (1974) was given by F. Boyce and Codd, which is known as the Boyce-Codd Normal Form (BCNF, which is 3.5NF) to distinguish it from the old definition of the third normal form. R. Faign introduced 4NF(1977) and 5NF(1979) and DKNF(1981). All the normal forms depend on functional dependency, but 4NF and 5NF have been proposed based on the concepts of multivalued dependency and joining dependency.

Hadoop MapReduce well explains the pain is writing too much code for simple MapReduce in Java. This organic blog explains how to use MRJob package in Python to write and execute Movie ratings.

After install the sandbox from the Hortonworks, you can visit the http://localhost:50070 page to find the information about the HDFS cluster. YARN job manager can be access via http://localhost:8088.

Java Futures are the way to support asynchronuous operations. Learn the basics of Java 9 Parallelism before read this post.

The CompletableFuture has been introduced since JDK 8 (2014). This is a abstraction over the `java.util.concurrent. Learn the basics of Java 9 Parallelism before read this post.