Write a First Capability

Start with one system responsibility. Avoid beginning with service names, database tables, or HTTP routes.

1. Name The Capability

Choose a verb phrase that describes the responsibility. In this guide, the responsibility is RegisterCustomer.

2. Define Intent

Intent says what initiates the capability. Here, a Customer provides RegistrationInput.

3. Name Outcomes

Outcomes should make meaningful paths explicit: RegistrationAccepted, TermsRejected, and VerificationDeferred.

4. Add Rules And Effects

The TermsAccepted rule guards acceptance. The effects describe registration persistence and a verification message, including the order between them.

5. Select Outcomes

The when block connects semantic conditions to outcomes. Rule violations and unresolved effects lead to different explicit outcomes.

language dcl 0.9

actor Customer is human

effect PersistRegistration is persistence
effect SendVerificationMessage is notification

shape RegistrationInput {
  email: Email required
  acceptedTerms: Boolean required
}

event VerificationMessageSent is {
  email: Email required
}

capability RegisterCustomer {
  intent RegistrationInput from Customer

  outcomes {
    RegistrationAccepted
    TermsRejected
    VerificationDeferred
  }

  rule TermsAccepted: input.acceptedTerms is true

  effects {
    PersistRegistration
    SendVerificationMessage after PersistRegistration
  }

  events {
    emits VerificationMessageSent
  }

  when {
    TermsAccepted violated then TermsRejected
    SendVerificationMessage unresolved then VerificationDeferred
    otherwise then RegistrationAccepted
  }
}

Open in Playground

Next Step

Read the register customer example for expected outcomes and concept notes.