Appendix C: Stdlib Kinds

The stdlib ships two packages of kinds. Bring them into scope with:

use * from arch.modules
use * from arch.kinds

Both packages auto-resolve against the toolchain’s bundled stdlib — no dependencies entry needed.

Module kinds (arch.modules)

Kind	Required blanks	Defaults	Default widget
service	required cascade team, required labels.domain	—	arch-service
frontend	required cascade team, required labels.domain	—	arch-frontend
database	required cascade team, required labels.data.classification	—	arch-database
component	—	cascade team	arch-component
system	—	cascade team	arch-system
external_system	required ext.vendor, required ext.contract.url	—	arch-external-system
actor	—	—	arch-actor

Reading the table:

• Required blanks must be filled or dropped by every instance.
• Defaults are pre-set fields the instance inherits (with cascade semantics where shown).
• Default widget is the custom-element tag the instance renders with (cascaded via cascade widget: ...).

A project that does use * from arch.modules gets working visuals for free — no widgets: script of its own required.

Facet kinds

The stdlib defines one facet kind: facet (the generic base kind, no defaults, no required blanks). Custom facet kinds (resource, capability, endpoint_group) are conventionally declared per-project. See Chapter 6 and Chapter 16.

Interface kinds (arch.kinds)

Kind	Parent	Semantic
sync	interface	Generic synchronous interface
async	interface	Generic asynchronous interface
command	sync	State-changing operation
query	sync	Read-only operation
event	async	Pub/sub broadcast
stream	async	Long-lived data stream

The two parent kinds (sync, async) drive edge styling: sync edges solid, async edges dashed. The four child kinds (command, query, event, stream) inherit that styling and convey the specific semantic.

Only event and stream (and anything subtyping them) are meaningful targets for subscribes: wiring.

Project-local kinds

Define your own kinds when domain vocabulary is preferred over the generic kinds. See Chapter 16.

// In your project's kinds.arch
export type service internal_service {
    required cascade team
    labels {
        security.zone: Internal
    }
}

Then use the kind anywhere in the package:

internal_service Authorize {
    team: Platform
    command Authenticate
}

To make a project-local kind visible to other packages, mark it export and import it via use … from <your.package> in their package.archspace.

See also

• Chapter 4: Modules — module kinds in depth
• Chapter 5: Interfaces — interface kinds in depth
• Chapter 16: Defining Kinds — declaring your own
• Chapter 20: Widgets — how kind widgets render