18.2 Item Coverage Settings, Positive/Negative Days, Time Fences, and Action Messages
Key Takeaways
- Item coverage overrides broad Coverage group rules at the released product level, enabling discrete minimum/maximum, lead time, and planned order types per Site and Warehouse.
- Positive days dictate how far into the future on-hand inventory or incoming receipts can satisfy upcoming demand; Negative days specify how long master planning will wait for an existing scheduled receipt before creating a duplicate planned order.
- Time fences define planning horizons: Coverage fence calculates requirements, Freeze fence locks planned orders, Firming fence auto-converts planned orders, and Explode fence governs multi-level BOM explosion.
- Action messages generate real-time operational advice (Advance, Postpone, Increase, Decrease) to align existing purchase, production, and transfer orders with fluctuating demand.
- Period templates divide the planning horizon into structured time buckets (days, weeks, months) for consolidated supply and demand visualization in Net Requirements and Supply Schedule forms.
18.2 Item Coverage Settings, Positive/Negative Days, Time Fences, and Action Messages
Quick Answer: While Coverage groups define baseline planning policies across groups of items, Item coverage (
Product information management > Released products > Plan tab > Item coverage) allows supply chain consultants to override parameters at the discrete product, site, and warehouse levels. Master planning schedules supply by evaluating Positive days (how long existing inventory can satisfy future demand) and Negative days (how long master planning will wait for an open receipt before generating a new order). Time fences establish execution horizons (Coverage, Freeze, Firming, Explode, Capacity, Action messages), while Action messages recommend advancing, postponing, increasing, or decreasing existing orders.
1. Item Coverage Architecture and Hierarchy
Organizations rarely maintain uniform replenishment rules across all distribution nodes. A product distributed from a central warehouse may require a Min/max policy with a 30-day coverage horizon, while regional transit cross-docks operate on a strict 2-day Requirement basis.
Item Coverage Configuration
- Navigation:
Product information management > Released products > Plan tab > Item coverage. - Item coverage records are created for specific combinations of inventory dimensions (typically Site and Warehouse).
+-------------------------------------------------------------------------+
| ITEM COVERAGE HIERARCHY |
+-------------------------------------------------------------------------+
| 1. Item Coverage: Specific Item + Site + Warehouse (Highest Priority) |
| │ |
| ▼ |
| 2. Item Coverage: Specific Item + Site (All Warehouses in Site) |
| │ |
| ▼ |
| 3. Item Coverage: Specific Item (All Sites / Global Item Level) |
| │ |
| ▼ |
| 4. Coverage Group assigned to Released Product |
| │ |
| ▼ |
| 5. Master Plan Default Coverage Settings (Lowest Priority) |
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Core Overrides on Item Coverage
- General FastTab: Override the default Coverage group, Coverage code, and Minimum/Maximum inventory levels.
- Planned Order Type: Specify whether master planning should generate a Planned purchase order, Planned production order, or Planned transfer order for that specific warehouse.
- Replenishment Warehouse: When Planned transfer order is selected, define the source shipping warehouse (e.g., Warehouse 11 transfers stock from Warehouse 10).
- Lead Time Overrides: Specify warehouse-specific purchase, production, or transfer lead times.
2. Mechanics of Positive Days vs. Negative Days
The interaction between Positive Days and Negative Days represents one of the most mathematically critical concepts on the MB-330 exam. Both settings can be defined on Coverage groups or overridden on Item coverage.
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| POSITIVE DAYS VS. NEGATIVE DAYS |
+-------------------+-----------------------------------------------------+
| Parameter | Operational Definition & Impact |
+-------------------+-----------------------------------------------------+
| Positive Days | The number of days into the future that on-hand |
| | inventory or expected receipts can satisfy a demand |
| | requirement before master planning creates a new |
| | planned order. Defines receipt viability. |
+-------------------+-----------------------------------------------------+
| Negative Days | The number of days past a requirement date that |
| | master planning will accept an existing scheduled |
| | receipt (e.g., purchase order) rather than ordering |
| | an expedited, duplicate planned order. |
+-------------------+-----------------------------------------------------+
Mathematical Deep Dive: Negative Days and the Duplicate Order Trap
Consider a company with the following scenario:
- Today: January 1
- Demand: Sales order for 100 units required on January 10
- Existing Supply: Open Purchase Order for 100 units scheduled to arrive on January 14 (4 days late relative to the demand)
- Purchase Lead Time: 5 days
Timeline: Today (Jan 1) -------- Demand (Jan 10) ---- PO Receipt (Jan 14)
▲ ▲
└────── 4 Days ───────┘
Outcome A: Negative Days = 5 (Greater than the 4-day delay)
- Master planning evaluates the gap:
Delay = 4 days. BecauseNegative days (5) >= Delay (4), master planning considers the existing Purchase Order acceptable. - Result: Master planning does not create a new planned purchase order. It pegs the sales order to the existing PO arriving on January 14 and generates an Action message (Advance) requesting the buyer pull the PO delivery date forward to January 10.
Outcome B: Negative Days = 2 (Less than the 4-day delay)
- Master planning evaluates the gap:
Negative days (2) < Delay (4). The existing PO is deemed too late to fulfill the demand. - Result: Master planning creates a NEW Planned Purchase Order for 100 units to meet the demand on January 10 (or earliest lead-time date). The existing PO of 100 units arriving January 14 remains open as excess inventory!
- Consequence: The organization now has 200 units of supply for 100 units of demand. Setting negative days too low causes widespread duplicate planned orders and excess inventory accumulation.
[!NOTE] Dynamic Negative Days in Planning Optimization: Planning Optimization can calculate dynamic negative days by comparing the item's purchase lead time against the scheduled arrival. If the scheduled receipt arrives sooner than placing a brand-new order from scratch, the existing receipt is used, preventing duplicate orders.
3. Master Planning Time Fences
Time fences establish operational horizons (expressed in days from today's date) that regulate what master planning is allowed to calculate, lock, or execute. Time fences can be configured on the Master Plan, the Coverage Group, or the Item Coverage record.
+-----------------------------------------------------------------------------------+
| MASTER PLANNING TIME FENCES |
+-----------------------------------------------------------------------------------+
| [ Today ] ──► [ Freeze ] ──► [ Firming ] ──► [ Explode ] ──► [ Coverage Fence ] |
| │ │ │ │ │ |
| │ No changes Auto-convert Explode BOMs Net requirements |
| │ permitted planned orders down levels horizon ends |
+-----------------------------------------------------------------------------------+
Comprehensive Time Fence Reference
| Time Fence | Primary Purpose | What Happens Inside Fence | What Happens Outside Fence |
|---|---|---|---|
| Coverage time fence | Defines the total planning horizon. | Master planning calculates net requirements, evaluates demand, and generates planned orders. | Demand (sales orders, forecasts) is completely ignored by master planning. |
| Freeze time fence | Prevents system nervousness and preserves planned schedule stability. | Existing planned orders cannot be deleted, rescheduled, or modified by regeneration runs. | Master planning dynamically reschedules and adjusts planned orders as demand shifts. |
| Firming time fence | Automates transition from planning to execution. | Planned orders are automatically converted (firmed) into actual Purchase Orders, Production Orders, or Transfer Orders during batch runs. | Planned orders remain suggestions awaiting planner intervention. |
| Explode time fence | Governs multi-level Bill of Materials (BOM) decomposition. | Production BOMs are exploded down through all sub-assembly levels, creating planned orders for raw materials. | Sub-assemblies are treated as purchased/discrete end-items; lower BOM levels are not exploded. |
| Capacity time fence | Controls finite resource capacity scheduling. | Production orders are scheduled against actual finite resource capacity and resource group limits. | Production orders are scheduled assuming infinite capacity. |
| Action message fence | Generates operational rescheduling recommendations. | Master planning generates Advance, Postpone, Increase, and Decrease action messages. | No action messages are generated, reducing notification clutter. |
4. Action Messages and Margin Tolerances
As business conditions shift, existing purchase orders, production orders, and transfer orders can drift out of alignment with customer demand dates. Rather than creating new orders, master planning issues Action Messages advising planners how to synchronize existing supply.
- Navigation:
Master planning > Setup > Coverage > Coverage groups > Action message tab.
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| ACTION MESSAGE TYPES |
+-------------+-----------------------------------------------------------+
| Action Type | Operational Meaning & Business Trigger |
+-------------+-----------------------------------------------------------+
| Advance | Move the delivery date of an existing open order forward |
| | (earlier) to satisfy an expedited demand or avoid stockout|
+-------------+-----------------------------------------------------------+
| Postpone | Delay the delivery date of an existing open order to |
| | prevent carrying unnecessary inventory holding costs. |
+-------------+-----------------------------------------------------------+
| Increase | Increase the order quantity on an existing order to cover |
| | newly created demand without issuing a new order. |
+-------------+-----------------------------------------------------------+
| Decrease | Reduce the order quantity on an existing order to avoid |
| | over-stocking caused by cancelled customer demand. |
+-------------+-----------------------------------------------------------+
Action Message Tolerances and Margins
To prevent planners from suffering alert fatigue from minor, inconsequential date shifts, consultants configure Action message margins:
- Advance margin: Minimum number of days an order must be advanced before generating an action message. If Advance margin is set to 2 days, a 1-day advance requirement will not trigger an alert.
- Postpone margin: Minimum number of days an order must be delayed before recommending postponement.
- Basis: Action messages can be calculated based on Requirement date, End of coverage period, or Today's date.
5. Period Templates
Period templates segment the continuous master planning timeline into discrete visual time buckets (e.g., daily buckets for the first 2 weeks, weekly buckets for the next 2 months, and monthly buckets for the remainder of the year).
- Navigation:
Master planning > Setup > Coverage > Period templates.
Structure and Application
- Planners define a sequence of periods with specific period lengths:
Day,Week,Month,Quarter, orYear. - Where Used: Period templates govern the time-phased grid displays in the Supply Schedule, Net requirements, and Capacity reservations forms.
- Operational Benefit: Provides executive and material planners with clear visibility into projected on-hand balances, aggregated gross requirements, and scheduled receipts without scrolling through thousands of individual transaction lines.
6. Implementation Scenarios and Exam Traps
[!IMPORTANT] Exam Tip — The Negative Days Duplicate Order Trap: Whenever an MB-330 exam question presents an issue where "master planning generates unnecessary duplicate planned purchase orders even though open purchase orders already exist for the required items," immediately inspect the Negative days parameter. If Negative days is smaller than the supplier delivery delay, master planning assumes the existing order is invalid and generates a redundant order.
[!WARNING] Exam Trap — Freeze vs. Firming Time Fences: Do not confuse Freeze with Firming. The Freeze time fence freezes planned orders as untouchable planned orders (status remains planned, but regeneration cannot alter them). The Firming time fence converts planned orders into actual transactional documents (Purchase Orders or Production Orders).
[!TIP] Best Practice — Explode Time Fence Tuning: Keep the Explode time fence shorter than the total Coverage time fence for complex manufacturing BOMs. Exploding 10-level BOMs out 365 days severely degrades planning performance and clutters raw material schedules with speculative requirements.
A company sells precision measuring equipment. On May 1, a sales order is entered for 50 units with a confirmed ship date of May 12. An existing purchase order for 50 units is currently open with a confirmed vendor delivery date of May 16 (4 days after the required ship date). The item's coverage group has a purchase lead time of 10 days, Positive days set to 30, and Negative days set to 2. When master planning executes, what will be the resulting planned order generation?
A production scheduling supervisor notices that every night when master planning runs, planned production orders that were carefully scheduled across assembly lines for the upcoming three days are continually deleted, rearranged, and rescheduled. The supervisor requires that planned orders within a rolling 3-day window remain completely untouched by master planning regeneration, but does NOT want them converted into released production orders until 24 hours prior to production. Which time fence configuration should the consultant implement?
A buyer receives notification that a customer increased their sales order requirement from 200 units to 350 units. An existing, confirmed purchase order for 200 units is currently open with the supplier, scheduled for delivery next week. The buyer wants master planning to evaluate the open purchase order against the expanded sales demand and suggest modifying the existing purchase order rather than creating a new planned purchase order. Which action message must be enabled on the coverage group?