Paths and area aggregation
/L5/A/ldk is not a name but an address. And the hierarchy cut by / is itself the unit of aggregation. A path plays two roles at once.
Those two roles dissolve a problem that has been awkward in architectural data for years — where to cut granularity. At rooms? At dwelling units? At storeys? koyu's answer is "at all of them; the path makes them hold simultaneously".
As an address
A path is human-readable. The outside world can point at a space without a table of UUIDs.
space /L5/A/ldk ldk X1..X3 Y1..Y2 name:リビングダイニングSensor readings, a booking system and a BEMS can all use the string /L5/A/ldk as a foreign key. The path is the meaning.
The leading segment of a path becomes a level only when a level of that name is declared. Writing /L1/ does not conjure a level into existence.
grid X 0 3600
grid Y 0 4000
space /L1/x room X1..X2 Y1..Y2✖ p3.muro:line 3: /L1/x has a region, but its level cannot be determined (give it at the head of the path or with level:)An error, not a warning; the exit code is 1. Without a level no form can be made, so this counts as missing sufficiency.
The head of a path can express only one level, so groupings that cross storeys (maisonettes and the like) are stated with the level: attribute.
As an aggregation hierarchy
A space with a region may not have child spaces with regions, because parent and child would overlap.
grid X 0 3600 7200
grid Y 0 4000
level L1 0 h:2400 slab:150
space /L1/home unit X1..X3 Y1..Y2
space /L1/home/a room X1..X2 Y1..Y2
space /L1/home/b room X2..X3 Y1..Y2✖ p1.muro:line 4: Space regions overlap: /L1/home and /L1/home/a
✖ p1.muro:line 4: Space regions overlap: /L1/home and /L1/home/bTo split a dwelling into rooms, make the parent a zone, not a space. A zone has no geometry; it is a counted aggregation that gathers whatever sits under its path prefix.
grid X 0 3600 7200
grid Y 0 4000
level L1 0 h:2400 slab:150
zone /L1/home name:住戸
space /L1/home/a room X1..X2 Y1..Y2
space /L1/home/b room X2..X3 Y1..Y2L1
/L1/home/a a room 14.40 m2
/L1/home/b b room 14.40 m2
Subtotal 28.80 m2
Total 28.80 m2 (indoor floor area)
By zone (counted aggregation):
/L1/home 住戸 28.80 m2The individual rooms come out, and the dwelling total survives. You can split into a layout without losing the language of the dwelling — that is what the double role buys.
From which one design guideline follows: put the unit you want to aggregate by nearer the head of the path.
The bundled examples use two idioms.
| Idiom | Examples | What you want to aggregate by |
|---|---|---|
/L1/room — level first | two-rooms, office, mansion, tower, complex | area per storey, checks per storey |
/home/room + level:L1 — dwelling first | house | area per dwelling, maisonettes |
Neither is better. It is a difference in what you want to group by. When to reach for zone rather than space is covered in zone.
Paths change, which is why uid exists
Rename or restructure and the path changes, and any sensor or register that used it as a foreign key loses its join.
When a reference must outlive the path, use uid:. It is an opaque token, unique across the model, and not derived from the path.
space /L5/A/ldk ldk X1..X3 Y1..Y2 uid:u-7f3k9m2qx4b8dhtvNot derived from the path is the crux. Derive it and a rename changes the token, and the whole point of a uid — pointing at the same thing across a rename — evaporates. When a machine makes one, it is random.
The division of labour is clean.
| Purpose | What to use |
|---|---|
references inside the repository (boundary, doors, zone totals) | the path |
| aggregation hierarchy | the path |
| long-lived identity across renames (sensors, survey, registers) | uid |
uid may be written on space and zone and nothing else. It cannot go on a relation because a relation's identity is derived from its two ends (Walls as boundaries). The details are in Identity.
It also works as a namespace
When composing several files, no per-layer namespace prefix is needed — the path hierarchy is already a namespace. Let L5.muro write /L5/... and core.muro write /B2..L19/core/... and nothing collides.
This is the result of borrowing from USD only the mechanism of a path namespace (Splitting and layering files).