Case · 04·Supporting·Procurement allocation

Header delta allocated with governance — line cost stays honest.

Header-level discounts, charges, and tax components stop corrupting line-level cost. Allocation is a governed rule, tax base follows the allocated line, and 3-way reconciliation happens at WBS — not at "report export".

PatternRule-driven allocation

GranularityHeader → Line → WBS

TaxMapped · not gross

Reconciliation3-way · by WBS

Allocation · header to line Traced

01Header

02Rule

03Line split

04Tax base

05WBS cost

Audit anchor · traceable back to source

PO doc

Line #

Rule ID

WBS

Sample scope20 POsAcross 4 projects

Line items79All with allocated deltas

Allocation bases3Value · quantity · none

WBS aggregations33Committed · received · invoiced

Demo exceptions7Routed by rule, by owner

Why this mattered

Totals looked right. Line-level cost told a different story.

Header discounts and charges stayed on the header. Line-level WBS cost drifted silently — invisible to anyone not reading the allocation logic by hand.

Operational problem

Header deltas corrupted the line — and no one saw it until month-end.

Header-level discounts (rebates, volume breaks) never made it down to the line. PMs read WBS cost without the rebate reflected.
Header charges (freight, inspection, handling) were spread informally or ignored — same line items carried different cost depending on who ran the report.
Tax base was computed against the raw line, not the governed line — so tax reconciliation drifted.
Reconciliation happened only at export: Excel, VLOOKUP, a coffee break, and a guess.

System & data gap

No governed rule for header → line, no anchor back to the document.

Allocation basis was implicit — nowhere in the data model. Rebuilding it required reading PO headers and line totals simultaneously.
No audit trail: if a variance was questioned later, tracing it to a specific rule version was impossible.
3-way matching stopped at quantity — no one was matching the allocated cost against receipt and invoice at the line level.
Exception routing was generic — "reconciliation owner" for every case, regardless of whether the problem was AP, procurement, or warehouse.

What I built

Three parts: the rule, the split, the anchor.

Allocation model · audit-safe Rule → split → tax base → WBS

01PO header

02Rule · versioned

03Line · allocated

04Tax base · mapped

05WBS · trusted cost

Every line stores its anchor

doc_id

line_no

rule_version

wbs_code

Logic & control

The rules that make allocation defensible.

Three control patterns turn a silent risk into a governed, auditable step.

Rule 01 · allocation basis

Value-proportional by default

Header discount splits by line value. High-value lines carry more of the rebate, low-value lines less — proportionally.

line_disc = header_disc × (line_value / Σ line_values)

Header-only

Line A · 1,000→ 1,000

Line B · 2,000→ 2,000

WBS carriespre-rebate

Allocated

Line A · 1,000→ 970

Line B · 2,000→ 1,940

WBS carriestrue net

Rule 02 · tax base

Tax follows the allocated line

Tax base = allocated line net (post-discount, plus allocated charges). Tax on the right number, every line, every time.

tax_base = line_value − disc_alloc + charge_alloc

Gross-based

Line taxon raw value

Driftmonth-end

Allocated-base

Line taxon allocated

Driftzero

Rule 03 · exception routing

Route by the rule that fired

Every exception carries its triggering rule ID. Tax mismatch → Finance Ops. Discount ceiling breached → Procurement. Receipt surplus → Warehouse.

owner = catalog[rule_id].owner

Generic

Owner"Reconciliation"

Fix timedays

Scoped

OwnerFinance Ops

Fix timesame-day

Traceability

A WBS cost line traces to a PO line, a rule version, and an allocation decision.

If leadership asks "why is A-2.3 reading 27,386 SAR?" — the answer walks back through five governed steps.

PO · 10421 · header → Rule · R-02 v14 → Discount allocated · -486 SAR → Tax base · 23,814 SAR → Tax · 3,572 SAR → WBS A-2.3 · 27,386 SAR

Invoice · INV-2026-8824 → Match · 3-way → Variance · +0.4% → Within tolerance → Auto-approve · posted

Outcomes as signals

What shifted in how procurement cost is read.

WBS costTrustworthyno silent drift

Tax reconciliationMappednot gross, not later

Audit trailPer line · per rulerule_id + version stored

Exception routingScoped by ruleright owner, first time

Artifacts

Proof artifacts — live and planned.

Excel · live

Procurement Truth · demo workbook

20 POs · 79 lines across 4 projects · 33 WBS aggregations · 7 realistic exceptions. Shows allocation rule, tax base mapping, and 3-way reconciliation by WBS — with integrity checks listed in the README sheet.

Download Excel → Available · portfolio sample

Excel · live

Cost Control · WBS Workbook

Complementary view: the committed / received / invoiced / actual / forecast model that sits on top of procurement truth. Same 4 projects; activity-level roll-up.