When customers implement Oracle dump during operational activity, it often produces inconsistent dump. It happens when a parent table got exported prior to it's child. In the dump the child table may contain "orphan" records. Such scenario leads to loosing a "Foreign Key" constraints when a dump gets restored on a test system. Loosing a Foreign Key constraint not just an introduction of a loose consistency. It also may lead to an index lost, because we automatically create indexes for all Foreign Key constraints. This may affect performance.
As a summary, we have to prevent such inconsistent state during an Oracle database dump and have a script to fix such inconsistency. Consistent data export can be done using regular Export utility or advanced Data Pump Export utility. This document describes recommended method and mentions other methods to implement consistent dump at the current moment.