The major integration is in MRP............ During MRP how the system should create procurement proposals..
MM & PP is integrated in follwoing ways :
1. BOM
2. when we issue material to production order
3. when we recived material against production order.
MM integration with PP
1.Purchase requisition creation from production order.
2.Goods receeipt for production order.
3.Goods movement from one operation to other.
4.creating the reservation for production orders..etc
Integration Points between PP and MM (Briefing)
原文：http://www.cnblogs.com/jefflu2012/p/4241901.html