One stock position across outlets that each kept their own books

Each outlet ran its till as an island. Stock counts drifted between locations, price changes had to be repeated by hand at every site, and tax treatment was worked out per invoice. Producing a consolidated position at month end meant reassembling numbers by hand from several sources, and any disagreement between them had to be settled by argument.

We are building a single domain model covering outlets, terminals, stock movements and tax, with the integrity rules held in the database so no client can write an inconsistent state. Stock is an append-only ledger of movements rather than a mutable quantity, making every position derivable and explainable. Tax is modelled as effective-dated rules applied at line-item level, so a rate change becomes a data change rather than a release.

1. NOTE.01

   Append-only stock ledger, so a position can always be reconstructed and explained

2. NOTE.02

   Effective-dated tax rules covering VAT and SSCL treatment, leaving historical invoices computing as issued

3. NOTE.03

   Idempotency keys on offline sales, letting a till retry aggressively without double-posting

4. NOTE.04

   Reporting served from a separate projection so month-end queries cannot slow a queue at the till

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  A consolidated stock position derivable without manual reassembly

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  Price changes applied once and propagated to every outlet

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  Tax rate changes handled as data, without a code release