MRP Outputs, Action Messages, and Exception Management
What MRP emits
Two families of output: planned orders (receipts and releases, with dates and quantities) and action messages. Planned orders feed CRP and become requisitions, work orders, or schedule agreements once firmed. Action messages tell the planner what to change: release now, expedite (reschedule in), de-expedite (reschedule out), cancel, increase or decrease quantity, check lead time, check BOM, check availability, plus past-due and negative-inventory exceptions.
Reading messages correctly
Reschedule-in means the need date moved earlier - pull the order forward. Reschedule-out means it moved later - push it back. Dates arriving past due mean the required date has already passed; the planner decides whether to expedite, substitute, or re-plan the parent. Firm planned orders are not modified by regeneration but are still exploded to their components.
Exception management
MRP generates far more messages than a planner can act on, so the craft is filtering: by item, planner, dollar value, and days late. Priority usually follows customer impact and remaining cumulative lead time. Pegging traces a component order back to the parent order and the demand behind it, which is how a planner decides which requirement to short.
Worked example
Component P shows a planned order release of 200 with a date in the past. MRP prints "release 200 now", pegged to an MPS order for 100 end items due in three weeks. The planner releases 200 on an expedited date, confirms the supplier can now deliver in two weeks instead of four, and updates the lead-time field - otherwise the same exception reappears at the next regeneration.
Traps
Treating every message as an instruction; a message is a proposal to be assessed. Confusing expedite with de-expedite. Ignoring a past-due release because the parent order is still distant. Letting exception volume grow by never correcting master data.