3.3 Reservation Hierarchies and Unit Sequence Groups

3.3 Reservation Hierarchies and Unit Sequence Groups

[!NOTE] In advanced Warehouse Management (WMS), inventory allocation cannot function like legacy ERP systems. Reserving inventory at sales order entry cannot lock specific physical storage bins or pallets weeks before shipment. To decouple commercial order promises from granular floor execution, Dynamics 365 Supply Chain Management utilizes Reservation Hierarchies (Warehouse management > Setup > Inventory > Reservation hierarchy) and Unit Sequence Groups (Warehouse management > Setup > Units > Unit sequence groups).

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The Architecture of Reservation Hierarchies: Solving "Bin-Locking"

In legacy warehouse management, when a sales order line reserved 50 units of an item, the system immediately reserved a specific Location (e.g., Aisle 04, Shelf 02, Bin 01) and a specific License plate (pallet). This created the infamous "bin-locking" problem:

• Forklift drivers could not consolidate or replenish inventory in that bin because the stock was reserved.
• Other urgent customer orders could not pick from that bin, even if the reserved order was not scheduled to ship for another three weeks.
• Warehouse floor agility was crippled.

The Reservation Hierarchy Solution

A Reservation Hierarchy defines the exact sequence in which inventory dimensions are reserved during the order lifecycle. It splits dimensions into two structural zones: Dimensions Above Location and Dimensions Below Location:

+---------------------------------------------------------------------------------+
|                         RESERVATION HIERARCHY ARCHITECTURE                     |
+---------------------------------------------------------------------------------+
|  DIMENSIONS ABOVE LOCATION                                                      |
|  - Reserved at: Sales Order Entry / Order Promising / Master Planning           |
|  - Scope: Site, Warehouse, Inventory status (and Batch if Batch-Above)          |
|  - Role: Guarantees commercial availability without locking physical bins       |
+---------------------------------------------------------------------------------+
|  ========================= PHYSICAL LOCATION BOUNDARY ========================  |
+---------------------------------------------------------------------------------+
|  DIMENSIONS BELOW LOCATION                                                      |
|  - Reserved at: Wave Processing / Work Creation / Mobile Device Picking         |
|  - Scope: Location, License plate (and Batch if Batch-Below)                    |
|  - Role: Determines optimal picking bin via Location Directives & FEFO/FIFO     |
+---------------------------------------------------------------------------------+

Mandatory Dimension Placement Rules

1. Above Location (Mandatory Minimum):
   • Site
   • Warehouse
   • Inventory status Rationale: The sales order must know which geographical site and facility will fulfill the shipment, and must reserve stock with an Available inventory status rather than blocked or damaged stock.
2. Below Location (Mandatory Minimum):
   • Location
   • License plate Rationale: Location directives allocate the specific bin when the wave executes. License plate represents the physical carrier or pallet, which is scanned or confirmed dynamically by the warehouse picker.
3. Architectural Invariants: Site, Warehouse, and Inventory status can never be moved below Location. License plate and Location can never be moved above Location.

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Batch-Above vs. Batch-Below Reservation Hierarchies

When tracking perishable, chemical, or regulated goods with batch numbers, the consultant must make a critical architectural decision: Should Batch number reside Above Location or Below Location?

1. Batch-Above Location Use Cases

• Contractual Specifications: An aerospace or defense customer contracts to purchase titanium fasteners exclusively from melt-lot B-9021.
• Potency / Active Pharmaceutical Ingredient (API): A pharmaceutical customer requires an exact chemical concentration available only in batch LOT-441.
• Customer Approval: The customer inspects and pre-approves batch samples prior to shipment.

2. Batch-Below Location Use Cases

• Fast-Moving Consumer Goods (FMCG): Retail grocery distribution where the customer wants 100 cases of milk, but does not care which batch number is shipped, provided it meets shelf-life requirements.
• Automated FEFO (First Expired, First Out): The sales rep reserves 100 units at Site 1, Warehouse 24, Status Available. When the order is released to the warehouse, the Wave processing engine and Location directives (configured with the Batch FEFO strategy) evaluate all inventory in the warehouse and automatically assign picking work from the bin containing the earliest-expiring batch.

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Unit Sequence Groups and Handling Units

Advanced WMS requires knowing how items are packaged and handled on the warehouse floor. Unit Sequence Groups (Warehouse management > Setup > Units > Unit sequence groups) define the hierarchy of packaging units and determine which handling units generate unique license plates.

+---------------------------------------------------------------------------------+
|                      UNIT SEQUENCE GROUP PACKAGING HIERARCHY                    |
+---------------------------------------------------------------------------------+
|  PALLET (PL)  -> 50 Cases / 600 Eaches  | [X] License Plate Grouping enabled    |
|       ^                                 | (Each pallet receives a distinct LP)  |
|       |                                                                         |
|  CASE (CS)    -> 12 Eaches              | [ ] License Plate Grouping disabled   |
|       ^                                 | (Cases move as un-grouped cartons)    |
|       |                                                                         |
|  EACH (EA)    -> Base Inventory Unit    | [ ] License Plate Grouping disabled   |
|                                         | (Smallest measurable unit)            |
+---------------------------------------------------------------------------------+

1. Structure and Ordering Rules

• A unit sequence group defines an ordered sequence from the smallest handling unit (Base unit) to the largest handling unit (e.g., Each -> Box -> Case -> Pallet).
• Every unit transition requires an active Unit conversion record (Product information management > Setup > Units > Unit conversions) defining the mathematical relationship (e.g., 1 Box = 10 Eaches; 1 Pallet = 50 Boxes).

2. License Plate Grouping Parameter

The License plate grouping checkbox on a unit sequence group line controls physical containerization:

• If checked on the Pallet unit, the system treats a pallet as a discrete handling unit requiring a dedicated License Plate ID upon receipt or movement.
• If unchecked on the Case and Each units, workers can pick individual cases or eaches from a pallet without generating new license plate identifiers for each individual box, preventing license plate table bloat.

3. Mobile Device Work Execution Impacts

• Unit Restrictability: Mobile device menu items can restrict picking or receiving to specific units defined in the sequence group (e.g., full pallet receiving vs. case break picking).
• Replenishment: Min/Max replenishment templates use unit sequence groups to trigger replenishment work in full pallet increments from bulk storage to case-pick forward locations.

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Hierarchy Association and Maintenance Rules

1. Association: A reservation hierarchy is assigned to a released product on the Warehouse management FastTab (Product information management > Products > Released products).
2. Validation: The system validates that the item's storage dimension group has Use warehouse management processes enabled, and that all tracking dimensions enabled on the tracking dimension group are included in the reservation hierarchy.
3. Immutability: Once inventory transactions (InventTrans) have been posted for an item, its reservation hierarchy cannot be modified or changed through standard UI forms. Changing a hierarchy requires zeroing out all on-hand inventory, canceling open warehouse work, or running data upgrade scripts.

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Exam Watch: Critical Traps and Configuration Tips

[!WARNING]

• Trap 1: Placing Batch number above Location for standard retail items. If you assign a Batch-Above hierarchy to standard goods, sales order entry operators will be forced to manually select or auto-reserve specific batches at order entry, breaking automatic FEFO wave allocation!
• Trap 2: Attempting to put License plate above Location. License plates represent physical containers located within a warehouse location; placing License plate above Location violates D365 SCM core schema rules.
• Trap 3: Forgetting unit conversions before creating unit sequence groups. A unit sequence group cannot be saved or assigned to an item if valid unit conversions between all sequence levels do not exist.
• Trap 4: Changing reservation hierarchies on active items. On the exam, if a question asks how to switch an active item from Batch-Above to Batch-Below, the answer involves closing open transactions and zeroing on-hand inventory, not simply changing a dropdown on the released product form.