Collections

Collections turn groups of things into first-class things. Because collection members are untyped wrefs, any thing can be a member — including shapes and shaped things. A collection is an ordinary named thing with a built-in shape, version history, and wref. Because collections are things, they can be the target of assertions through the standard about field.

Collection Types

Type	Ordered?	Unique?	# of Members	Field Names
Arc	yes	yes	exactly 2	from, to
Bond	no	yes	exactly 2	ends
Set	no	yes	1+	members
List	yes	no	1+	items

The built-in collection shapes (Arc, Bond, Set, List) are auto-created on first use. You create and revise collection instances as ordinary named things.

Creating Collections

Every collection needs a user-chosen name. Names are not generated from the members.

wh collection create --type arc --name cave-route \
  --members Location/A,Location/B \
  -m "Create directed cave route" \
  --repo myorg/world

The same operation can be submitted through the generic commit surface:

wh commit submit --ops '[
  {
    "operation": "add",
    "kind": "collection",
    "type": "arc",
    "name": "cave-route",
    "members": ["Location/A", "Location/B"]
  }
]' -m "Create directed cave route" --repo myorg/world

SDK and MCP callers use the same model: add a named collection thing, then refer to that collection by wref.

await client.collection.create("myorg", "world", {
  type: "arc",
  name: "cave-route",
  members: ["Location/A", "Location/B"],
  message: "Create directed cave route",
})

Selector-Backed Sets

Set collections can be created from the same query mechanics used by thing queries. This is useful when the membership is “everything matching this selector” at a point in time.

Replace your-org/your-repo in the examples below with the slug of the repo you are writing into.

wh collection create --type set --name wake-voters \
  --shape Voter \
  --where county=Wake \
  --where state=NC \
  -m "Snapshot Wake County voters" \
  --repo your-org/your-repo

To build a collection in one repo from things in another repo, pass the source repo. The stored members are pinned refs to the source things.

wh collection create --type set --name wake-voters \
  --source-repo your-org/source-repo \
  --shape Voter \
  --where county=Wake \
  --repo your-org/your-repo

Selector-backed creation is set-only. Arc, Bond, and List require explicit members because their roles or arity are part of their meaning.

Asserting About Collections

about accepts a wref. It does not accept inline collection objects.

Create the collection first, then point the assertion at it:

wh commit submit --ops '[
  {
    "operation": "add",
    "kind": "collection",
    "type": "arc",
    "name": "cave-route",
    "members": ["Location/A", "Location/B"]
  },
  {
    "operation": "add",
    "kind": "assertion",
    "name": "Distance/cave-route",
    "about": "Arc/cave-route",
    "data": { "value": 5 }
  }
]' -m "Record route distance" --repo myorg/world

You can also create the collection in one command and later assert about Arc/cave-route.

Version Pinning

Collection members are pinned at write time. Bare member wrefs and @HEAD resolve to exact versions when the collection is created or revised:

{
  "operation": "add",
  "kind": "collection",
  "type": "set",
  "name": "audit-scope",
  "members": ["Location/A", "Location/B@HEAD", "Location/C@v2"]
}

The collection’s body stores pinned member refs. Retracting or renaming a member does not change the snapshot.

Revising Collections

Collections are revisable because they are ordinary named things. A new version of the collection records the new membership.

wh collection revise Set/audit-scope \
  --members Location/A,Location/C \
  -m "Refresh audit scope" \
  --repo myorg/world

Pinned collection wrefs act as revision guards. Revising Set/audit-scope@v1 fails if the live collection is already at a different version.

Reading Collections

Use the collection domain for collection operations:

wh collection members Set/audit-scope --repo myorg/world
wh collection contains Set/audit-scope Location/A --repo myorg/world
wh collection diff Set/old-scope Set/new-scope --repo myorg/world
wh collection stats Set/audit-scope --repo myorg/world

wh thing view still works because a collection is a thing. For large Set/List bodies, thing reads may return a compact collection summary instead of the full member array. Use --data-mode full when you need the canonical JSON body:

wh thing view Set/audit-scope --repo myorg/world
wh thing view Set/audit-scope --data-mode full --repo myorg/world

Normalization Rules

Set: members are deduplicated and sorted lexicographically.
List: order is preserved and duplicates are kept.
Arc: exactly two distinct endpoints; order is preserved as from → to.
Bond: exactly two distinct endpoints; endpoints are sorted so input order does not matter.

Modeling Guidance

Anchor an assertion about an Arc or Bond when the assertion describes a relationship that only makes sense with both endpoints. Use a single thing when the assertion is only about that thing.

Use Arc for directional relationships:

{
  "operation": "add",
  "kind": "collection",
  "type": "arc",
  "name": "alice-trusts-bob",
  "members": ["Player/alice", "Player/bob"]
}

Use Bond for symmetric binary relationships:

{
  "operation": "add",
  "kind": "collection",
  "type": "bond",
  "name": "alice-and-bob-are-teammates",
  "members": ["Player/alice", "Player/bob"]
}

Use Set when membership matters but order does not. Use List when order or duplicate membership is meaningful.