Examples

Systems and the lines between them, drillable level by level

• Atlas ShopGlobal event-sourced order shop. Commands append immutable events to a regional event store, Kafka carries the stream, projections build eventually-consistent read models, and MirrorMaker 2 mirrors events between regions. The diagrams show one regional stamp (EU); the US region runs the identical topology.4 diagrams · 22 elements · 20 relationships
• Order ShopA deliberately small model of one flow: a customer places an order in an online shop.3 diagrams · 18 elements · 15 relationships

Who calls whom, in order, over time

• Checkout — Place OrderOne order placed: card charged, order stored, receipt sent.5 participants · 11 messages
• Password reset — one-time linkA reset that survives a lost inbox: the link is single-use and the old session dies.5 participants · 14 messages

Steps, decisions and the loops back

• Checkout paymentOne order charged: validate the cart, take payment with one retry, record the outcome.10 steps · 11 arrows · 2 decisions
• Incident triageWho looks at an alert, and when it stops being one person's problem.10 steps · 12 arrows · 3 decisions

Who can do what at the system's edge

• Food deliveryWho does what at the system's edge: guests browse, customers order and track, couriers deliver — and every order includes payment.3 actors · 5 use cases · 1 boundary
• Hotel bookingTwo systems share one stay: guests book online, staff run the front desk — and the specialised actors inherit everything the general ones may do.4 actors · 5 use cases · 2 boundaries

What you store, and how one record finds another

• Shop orders5 tables · 16 columns · 4 relationships
• Course catalogueA join table whose key is entirely foreign, a course that requires another course, and enrolments that outlive a term.4 tables · 14 columns · 4 relationships

What each field means, and where its value comes from

• Customer APIEvery field the customer endpoints return, what it means, and where it comes from2 sections · 8 fields · 8 described
• order.placed eventThe envelope and payload every downstream consumer subscribes to — a contract with no table behind it.2 sections · 8 fields · 7 described

How long each piece takes, and what can't start until it's done

• Order store migrationMoving orders off the legacy store, and what blocks what9 tasks · 2 milestones · 39 days
• Frankfurt hall moveEmptying hall 2 into the new cage, and what cannot start until it is done9 tasks · 2 milestones · 55 days

What happened when, and which period it happened in

• How the platform grewTen years of the product, and the order it happened in4 periods · 11 events · 5 explained
• The checkout outageWhat happened on 3 March, in the order it happened4 periods · 10 events · 5 explained

What one thing went through, and where it can end up

• An order, from checkout to the doormatOne order, the states it passes through, and the two ways it can leave the trackOrder · 5 states · 2 end · 1 return
• A manuscript, from submission to printOne submission, the states it passes through, and every way it can leaveManuscript · 6 states · 2 end · 2 return

What breaks down into what, all the way down

• Account recovery reviewsA supervisor review queue, decomposed into the cases that prove it.3 levels deep · 6 of 10 are leaves · 2 columns
• Platform team, by what it ownsAn ownership breakdown with no columns — the plain shape of the notation.4 levels deep · 9 of 16 are leaves · no columns