Sequence view

The sequence view draws a scenario as a sequence diagram: one lifeline per node, one arrow per step, time running down the page. It suits readers who think in lifelines, and it is the quickest way to see who talks to whom, and in what order.

ScenarioOverviewPay with a cardCard declined

The shopper pays. We write the payment down first, charge the card second, and tell the rest of the system last, so a crash never loses money.

IRecord itbefore any money moves

1

Web app→Payments APIPOST /payments

The request carries an idempotency key, so a retry cannot charge twice.

2

Payments API→Ledger databaseINSERT payment (pending)

IICharge the card

3

Payments API→Stripecreate payment intent

4

Stripeauthorise card

This is the only step we do not control, and the slowest one.

5

Stripe→Payments APIsucceeded

IIIFinish

6

Payments API→Ledger databasemark paid

7

Payments API→RabbitMQpayment.succeeded

8

Payments API→Web app201 Created

9

RabbitMQ→Receipt mailerpayment.succeededplanned

Receipts are planned. Today the shopper only sees the on-screen confirmation.

Web app

Payments API

:8080

Ledger database

Stripe

card processor

RabbitMQ

payment.events

Receipt mailer

planned

Pick Sequence beside the player to switch any scenario to it, or open a scenario that way:

scenarios:
  pay:
    title: Pay with a card
    mode: sequence

<Diagram name="payments" scenario="pay" mode="sequence" />

How it is drawn

• Lifelines are the nodes the scenario uses, left to right in the order they first appear. Each heads its column with its icon, title and sub.
• Arrows are flow steps, drawn from the sender to the receiver with the step’s label above the line. The line style follows the step’s kind: solid for requests, dashed green for responses, red for errors, dotted grey for lookups and amber for events. A planned step is dashed.
• Self steps are drawn as a small labelled box on the node’s lifeline.
• Phases become labelled bands across the diagram, such as “I · Record it”.
• Numbers at the left match the numbers in the step list.

A step that crosses several nodes is drawn as one arrow from the first node to the last. The nodes in between do not get arrows of their own, because the sequence diagram shows what the scenario says, not the route a packet takes. Use the flow view to see the hops.

Playing it

The player works the same way in every view. Click a row to play that step, press Play to run the scenario, or use the scrubber. The row in progress is highlighted.

When to use it

You want to	Use
Show the architecture and how a request moves through it	Flow
Show who talks to whom, and in what order	Sequence
Walk a newcomer through what happens, in words	Story

All three come from the same steps, so there is nothing to keep in sync.