+In the *xacml-pdp* and *drools-pdp*, an *application* is written for a given category of policy types. Such an
+application may have logic written in Java or another programming language, and may have additional artifacts such
+as scripts and SQL queries. The *application* unmarshals and marshals events going into and out of policies as well
+as handling the sequencing of events for interactions of the policies with other components in ONAP. For example,
+*drools-applications* handles the interactions for operational policies running in the drools PDP. In the
+*apex-pdp*, all unmarshaling, marshaling, and component interactions are captured in the state machine, logic, and
+configuraiton of the policy, a Java application is not used.
+