Implementing Persistence and Transactions - jBPM6 Developer Guide - page 256

Here, we can see that we have two implementations of a KieSession interface:
StatefulKnowledgeSessionImpl , which is the real implementation of a KIE ses-
sion, and CommandBasedStatefulKnoweldgeSession , which is the command
pattern adaptation of the KIE session interface. The latter will implement each method by
creating a specific Command object and assigning its execution to a CommandService
object.
The actual implementation used by the JPA persistent KIE session is called
SingleSessionCommandService , and it provides a wrapper around the KIE ses-
sion command execution that creates a database transaction before the command execu-
tion, serializes the actual KIE session object to a persistent object, and commits the trans-
action.
The SingleSessionCommandService session doesn't directly implement the trans-
action management, but it has an Interceptor list that defines all the different method
decorations needed, similar to the way the Human task component explained in Chapter 6 ,
Human Interactions uses.
Eventually, the interaction between persistence and the KIE session activity happens on a
per-method invocation basis, as shown in the following diagram: