Here are the most common set of business requirement to support product level replenishment within a given facility(store/warehouse) via any inter-company facility (preferred warehouse/stocking facility) before raising the purchase order from an outside vendors/suppliers.

In current standard OFbiz workflow there are essentially two basic types of material requirements generated at product-facility level. Both of these can be created manually or could be suggested by MRP engine:

• First, is "Product Requirement" which suggests that the given product is going to be low or out of stock within any given facility in a given time frame based on upstream demand signals within the supply chain and hence can more commonly be treated as Purchase Requirement that need to be eventually transformed as Purchase Orders to be raised from a given vendor/supplier
• Second, is "Internal Requirement" which suggests that the given product is going to be low or out of stock within any given facility in a given time frame based on upstream demand within the supply chain. But such products can be internally manufactured(produced) and hence can more commonly be treated as Production Requirement that need to be eventually transformed as Production Order (Production Run).

Gap
Currently the OFbiz planning algorithm (aka MRP) generate the requirement by only considering the supply available within the given facility. But there is no planning logic built into the system which can support and look up the supply availability in a complex supply chain setup where business could be run using multiple facilities spread geographically. A more common examples could be brick and mortar retail stores chain having multiple stores spread across geographically. Or any manufacturing business that own multiple production facilities and warehouse spread across geographically.

Requirement
There are many instances, where material visibility in a multi-facility setup within an organization or company is not very accurately gauged. We would need to start building an intelligent planning system that could gauge such material availability across facilities and honor them while furnishing the requirements around any product within any given facility. 
Let's consider following use case (Please refer to attached screenshot for reference)

• A retail chain has multiple stores and say a given physical store 'Store_01' and is strategically located near two warehouse in the region say Whse_01 & Whse_02,
• One centralized warehouse(Main/buffer) say 'Backup_Whse' that supplies material to all the stores and regional warehouse
• Any retails store e.g. Store_01 shouldn't raise purchase order from any outside vendor directly.
• As Store_01 is strategically located near Whse_01 & Whse_02, so system should always suggest to replenish any product shortfall by first looking up and pulling up available supply from Whse_01 & Whse_02 and then from Backup_Whse in that order of priority.
• Banckup_Whse mostly works on push system and supplies the products to all regional warehouse and physical stores.

Now we could design an OFbiz based replenishment planning that :

• Could allow to associate and rank the facilities(physical store/warehouse) that could replenish the material at any other facility (physical store/warehouse)
• Could suggest the "Transfer Requirement" by gauging the product shortfall within any given facility product-facility at any given point of time by
• Could allow to configure and manage the setting at facility(ProductStore or ProductFacility) level, to let planning engine know whether given facility could replenish stock via Transfer Requirement from any other facility. If not then it could take normal route of replenishment via Purchase Order or Production Order route.