Workflows expressed in Oozie can contain:

A.
Sequences of MapReduce and Pig. These sequences can be combined with other actions
including forks, decision points, and path joins.

B.
Sequences of MapReduce job only; on Pig on Hive tasks or jobs. These MapReduce
sequences can be combined with forks and path joins.

C.
Sequences of MapReduce and Pig jobs. These are limited to linear sequences of actions with
exception handlers but no forks.

D.
Iterntive repetition of MapReduce jobs until a desired answer or state is reached.

Explanation:
Oozie workflow is a collection of actions (i.e. Hadoop Map/Reduce jobs, Pig jobs)
arranged in a control dependency DAG (Direct Acyclic Graph), specifying a sequence of actions
execution. This graph is specified in hPDL (a XML Process Definition Language).

hPDL is a fairly compact language, using a limited amount of flow control and action nodes.
Control nodes define the flow of execution and include beginning and end of a workflow (start, end
and fail nodes) and mechanisms to control the workflow execution path ( decision, fork and join
nodes).
Workflow definitions
Currently running workflow instances, including instance states and variables
Reference: Introduction to Oozie
Note: Oozie is a Java Web-Application that runs in a Java servlet-container – Tomcat and uses a
database to store: