Coordination between the PPBE process and Defense Acquisition System may be complicated because:  

• The PPBE process is driven by dates while the Defense Acquisition System is driven by events
• The PPBE is managed by DoD while the Defense Acquisition System is managed by the Components
• The PPBE process is driven by politics while the Defense Acquisition System is driven by facts
• The PPBE process is driven by events while the Defense Acquisition System is driven by milestones.