Modules, Features and Slices

Module

The module is the top-level namespace and maps to a bounded context. One module per file is the convention but not enforced.

module <Name>
  [description "<text>"]

  [<screen templates>]
  [<dialog templates>]
  [<features>]

Screen templates and dialog templates declared at module level are described in Layouts and templates.

Features

Features are vertical slice groupings. They nest arbitrarily deep for sub-features.

feature <Name>
  [description "<text>"]
  [feature <Name>]*   ← sub-features
  [slice <type> <Name>]+

Slices

The slice is the atomic unit of behavior, aligned with Event Modeling. A slice has a type and a name, and contains the constructs that implement the behavior.

slice <SliceType> <Name>
  [description "<text>"]
  [file <path>]
  <constructs>

The optional file line names the repository relative file this declaration is realized by, so a document can be navigated back to the code it describes. It is additive - it never stands in for any part of the declaration. See File references.

Descriptions

Modules, features, slices, personas, and commands take an optional description as their first body line — a human-readable summary consumers such as Prologue surface when presenting the model. At most one per declaration.

module Invoicing
  description "Everything related to invoicing customers"

  feature InvoiceManagement
    description "Registering and managing the lifecycle of invoices"

    slice StateChange RegisterInvoice
      description "Registers a new invoice"

When one line is not enough, use a fenced block — the same ``` convention as inline code blocks. The fenced text is kept verbatim:

module Invoicing
  description
    ```
    Everything related to invoicing customers.
    Registration, lifecycle and payment tracking of invoices.
    ```

Slice types

Type	Description
StateChange	A command → events flow; something that changes the system
StateView	A query + projection + screen; something that reads the system
Automation	A reaction or reducer; something that runs when something happens
Translate	A capture; converts external data into events

What goes in a slice

Construct	Typical slice type	Page
event	any	Events
command	StateChange	Commands
constraint	StateChange	Constraints
query	StateView	Queries
readmodel	StateView	Read models
projection	StateView	Projections
reducer	StateView	Read models
screen	StateView	Screens
reaction	Automation	Reactions
capture	Translate	Captures

Every one of these may appear as many times as the behavior needs — several events, several commands, several projections. Only description is limited to one. A slice is one behavior, not one artifact of each kind.

Example

module Invoicing

  feature InvoiceManagement

    slice StateChange RegisterInvoice
      command RegisterInvoice
        ...
      event InvoiceRegistered
        ...

    slice StateView InvoiceList
      query ListInvoices => InvoiceListReadModel[]
      projection InvoiceList => InvoiceListReadModel
        ...
      screen InvoiceList
        ...