Glossary

Key terms used throughout the domain definition language.

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Domain Building Blocks

Entity

A thing with identity and a lifecycle. Two entities with the same attributes but different identities are different things. Identity is defined separately in a .key file.

Example: Two children named "John Smith" born on the same day are still different children — they have different ChildId values.

Value Object

A thing defined entirely by its attributes. Has no identity. Immutable — if you need to change it, you replace it.

Example: An address. If you move, you don't update the address — you have a new address.

Union Type

A value with multiple possible shapes (variants). Only one variant is active at a time. The generator selects the appropriate variant based on infrastructure configuration.

Example: An image can be stored as binary bytes (Embedded) or as a reference to an external storage service (Reference), depending on the target database.

Standard Library

A set of pre-defined .value and .union files shipped with Modeller in the lib/ folder. These define canonical representations for commonly-used domain concepts such as monetary amounts, percentages, geographic coordinates, images, and documents. Use them by type name — the generator resolves their structure automatically.

Examples: money, percentage, geospatial, image, document.

Shared Data

Data that is used by this service but owned and managed by another bounded context. Read-only from this service's perspective.

Two kinds exist: global lookup tables (static reference data like countries or reason codes, not owned by any specific service) and per-consumer projections (a bounded view of another service's entity, containing only the fields this consumer needs, named {Entity}For{Consumer}).

Example: OrganisationForScheduling is a projection of the Organisation entity containing only the Name field, as needed by the Scheduling service.

Service

A collection of related entities, enums, and cross-service dependencies that together represent a business capability. Also called a "bounded context".

Example: The Scheduling service owns Booking, Attendance, and Session entities.

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Behaviours

Command

A business action that changes something. Named using action verbs.

Examples: "Place a booking", "Cancel an enrolment", "Record attendance"

Query

A business question that retrieves information without changing anything.

Examples: "Show today's bookings", "List children at centre", "Get attendance report"

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Events

Events signal that something has happened. Always named in past tense.

Domain Event

Something significant that happened within this domain. Other parts of the same domain may react to it.

Example: AttendanceRecorded — the Billing component might react to calculate charges.

Integration Event

A notification sent to other domains or external systems. Represents a contract with the outside world.

Example: ChildEnrolmentChanged — sent to government reporting systems.

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Relationships

Belongs To

Indicates ownership. The child entity's lifecycle is tied to the parent — if the parent is removed, so are its children.

Example: Attendance belongs to Booking — if the booking is removed, its attendance records go with it.

Has One / Has Many

Indicates association with another entity within the same service. has_one for a single related entity, has_many for a collection.

Example: Booking has many Attendances. Booking has one Session.

Has One? (Optional)

A has_one relationship where the related entity may not exist.

Example: has_one Absence? — a booking may or may not have an associated absence record.

References

A cross-service read dependency. The entity reads data from another bounded context's per-consumer shared type. The relationship is ID-only at the domain level — full navigation is not available within this service.

Example: references OrganisationForScheduling — the Booking entity reads the organisation's name from the Scheduling service's projection of Organisation data.

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Data Concepts

Projection

A view of data shaped for a specific query purpose. May combine fields from multiple entities. Defined in .projection files.

Example: "Attendance Report" projection combines Booking, Child, and Attendance data into a flat view for display.

Lookup

A global shared type used for selection or validation. Presented as dropdown lists or option sets in UIs.

Example: List of absence reasons, care types, or states.

Per-Consumer Projection

A .shared file that represents a subset of another service's entity, containing only the fields this consumer actually needs. Named {Entity}For{Consumer}.

Example: ChildForKiosk contains only FirstName, LastName, and Image — the fields the Kiosk service needs when displaying a child at sign-in.

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Technical Terms (for implementers)