Inventory does not live in isolation.
Purchasing brings product toward the warehouse. Sales consumes demand from the warehouse. Inventory sits in the middle trying to explain what is available, committed, expected, and moving.
Purchase Order Represents Supply
Purchase Order activity can represent material expected from vendors and eventually received into inventory.
Sales Order Represents Demand
Sales activity can reserve, ship, invoice, backorder, return, or otherwise change the operational picture around an item.
Inventory Provides the Shared Item and Warehouse Context
Sage's distribution materials describe Inventory Management, Inventory Requirements Planning, Purchase Order, Sales Order, barcode mobility, and RMA as an integrated distribution environment.
That integration is why an inventory question may actually begin in purchasing or sales.
Follow the Transaction Across Modules
When an availability or quantity question looks strange, we want to know what is on order, what is committed, what has actually been received or shipped, and which warehouse is involved.
The modules make more sense when treated as one distribution cycle instead of separate islands.