Supersession Chain

A supersession chain enforces a one-way substitution flow from the obsolete item to the successor. The ATP engine automatically redirects demand from the discontinued SKU to the active replacement, but never reverse-substitutes the new item with the old one. This prevents the accidental consumption of legacy inventory when the successor is available. The chain is typically defined with a directionality flag (e.g., 'A is superseded by B') in the material master, ensuring the planning engine respects the chronological product lifecycle.

Supersession chains support two operational modes:

• Full Supersession: The discontinued item is entirely replaced. All demand, including existing sales orders and forecasts, is immediately redirected to the successor upon the effective date.
• Partial Supersession: The old item can still be sold or consumed until inventory is exhausted, but new demand is preferentially directed to the replacement. This is critical for run-out strategies where remaining stock must be depleted before the switch is complete. The ATP engine evaluates available inventory of the old item first, then falls back to the successor.

A supersession chain is not limited to a single replacement. It can form a linear sequence spanning multiple product generations (e.g., SKU-A → SKU-B → SKU-C). When the ATP engine encounters a demand for SKU-A, it traverses the entire chain until it finds an active, available item. This recursive substitution ensures that even if intermediate successors are also discontinued, the system automatically resolves to the final, currently active product. Chain integrity checks prevent circular references.

Supersession relationships are governed by effective dates. A chain entry specifies the exact date and time when the substitution becomes active. Before this date, the ATP engine treats the items as independent. After the effective date, the substitution logic engages automatically. This allows supply chain planners to stage product transitions in advance, aligning the system's promising behavior with marketing launch dates and engineering change orders (ECOs) without manual intervention.

A robust supersession chain distinguishes between full interchangeability and directional replacement. Fully interchangeable parts (form-fit-function identical) allow bidirectional substitution, often used in service parts management. Directional supersession implies the new item is a superior or compliant replacement but the old item cannot substitute back. This distinction is critical in regulated industries like aerospace and medical devices, where using an obsolete part in place of a certified successor is prohibited.

When a supersession chain is invoked during an ATP check, the resulting demand pegging traces the requirement to the actual supplying item, not the originally requested one. This maintains full auditability: the system records that Customer Order X for SKU-A was fulfilled by SKU-B. This pegging transparency is essential for lot traceability, warranty claims, and analyzing the true consumption patterns of successor products during a transition period.