Audit Trail & Compensating Strategies

The Purchases & Procurement domain is designed to satisfy procurement audit requirements, internal control frameworks, and supplier relationship governance. Authorized commitments are immutable, and all corrections follow formal compensating strategies.

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1. Immutability of Authorized Commitments

Purchase Orders and Vendor Bills are locked once approved. Modifications require formal Change Orders or supplementary Debit/Credit Notes rather than record overwrites.

Locked Fields After PO Approval

Field	Modification Rule
Supplier	Cannot be changed; requires cancellation and reissue.
Item and UOM	Cannot be changed; requires change order or new PO.
Ordered Quantity	Cannot be increased; decreases require change order if no receipt exists.
Agreed Price	Cannot be changed; corrections require debit/credit note.
Delivery Date	Can be amended by mutual agreement with audit reason.
Cost Center	Cannot be changed; budget impact is fixed at approval.

Change Order Rules

• A Change Order is a separate document that references the original PO.
• It passes through the same approval matrix as the original PO.
• Once approved, it amends the commitment while preserving the original PO history.
• Change Orders cannot alter already-received quantities or matched bills.

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2. Correction Through Supplementary Documents

Erroneous or changed commitments are never deleted. The domain supports three compensating strategies:

Strategy	Use Case
Change Order	Modify quantities, dates, or terms of an approved PO before full receipt.
Debit Note	Reduce payables for returns, rejected goods, or price overcharges.
Credit Note	Accept a supplier correction reducing the amount owed on a vendor bill.

Correction Chain Example

Original PO #2000          Change Order #2000-1        Debit Note #DN-045
(Initial commitment)       (Quantity increase)          (Return of defective lot)
       |                           |                            |
       └───────────────────────────┴────────────────────────────┘
                          Commitment History

Every correction document references its predecessor, ensuring complete traceability for auditors and supplier dispute resolution.

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3. Vendor Rating & Quality Feedback

The domain systematically logs fulfillment reliability, delivery delays, and quality rejection rates to support supplier scorecards and sourcing decisions.

Metric	Definition
On-Time Delivery Rate	Percentage of PO lines received on or before the promised delivery date.
Quantity Accuracy	Percentage of receipts matching ordered quantity within tolerance.
Quality Rejection Rate	Percentage of received quantity rejected during inspection.
Price Variance Frequency	Frequency of vendor bills exceeding PO price tolerance.
Quote Responsiveness	Average time for a supplier to respond to an RFQ.

Scorecard Usage

• Scorecard results influence supplier status transitions (e.g., Prospect → Approved → Preferred).
• Poor performance may trigger On-Hold or Blacklist status.
• Preferred suppliers receive prioritization during automated supplier selection.

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4. Summary

The Purchases & Procurement domain in Obelaw is a rigorous, event-driven bounded context that enforces sourcing governance through 3-way matching, commitment integrity, approved vendor lists, and immutable audit trails. It remains isolated from Inventory, Accounting, and Customer contexts via an Anti-Corruption Layer and emits only the procurement events necessary to coordinate inbound logistics and financial settlement.