This project contains several diagrams describing Apache Hadoop internals (2.3.0 or later). Even if these diagrams are NOT specified in any formal or unambiguous language (e.g., UML), they should be reasonably understandable (here some diagram notation conventions) and useful for any person who want to grasp the main ideas behind Hadoop. Unfortunately, not all the internal details are covered by these diagrams. You are free to help :)