# title
Building Understanding Standard - Core Datatypes and Classes

# description
BUS-1 v0.2 core datatypes, entity base, and normative entity classes, including the portable presentation model. Provisional schema URIs pending establishment of the governance body.

# $defs.Id.description
An absolute URI that durably identifies an entity. urn:uuid form is RECOMMENDED, using UUID version 7 (RFC 9562).

# $defs.LocalId.description
Human-meaningful identifier, unique within an exchange package. Not a reference target.

# $defs.Timestamp.description
RFC 3339 date-time with a mandatory offset. An RFC 9557 IXDTF suffix MAY be appended.

# $defs.Quantity.description
A numeric magnitude with a unit code. See BUS-1 7.4 and Annex C.

# $defs.Quantity.properties.unitCode.description
A code from the BUS unit vocabulary, or from the system named by unitSystem.

# $defs.Quantity.properties.unitSystem.description
The vocabulary unitCode is drawn from. Default bus.

# $defs.Value.description
A property or binding value: a scalar or a Quantity.

# $defs.Classification.description
A classification in a taxonomy defined outside this specification. Preserved verbatim, never interpreted.

# $defs.Agent.description
An acting party recorded inline. Where the party is addressable, reference a bus:Party instead.

# $defs.Versioning.description
Envelope versioning. Object revision supports synchronization and merge, not only history.

# $defs.Versioning.properties.revision.description
Monotonically increasing per entity. Incremented on any change to the entity.

# $defs.PropertyValue.description
An intrinsic property value. Every property MUST reference a bus:PropertyDefinition; bare key-value data is not permitted.

# $defs.Entity.description
Abstract base for every addressable object. An entity carries only facts intrinsic to itself; contextual facts are relationships.

# $defs.Entity.properties.abstractTypes.description
Ancestor classes of this entity's type, most specific first. Lets a receiver place an entity whose leaf class it does not recognize.

# $defs.PropertyDefinition.description
Declares the meaning of a property name. REQUIRED for every property an exporter emits.

# $defs.PropertyDefinition.allOf[].properties.origin.description
Where the definition came from. Affects how much a receiver should trust it.

# $defs.Party.description
A person or organization with a role in the building.

# $defs.Building.description
The unit of ownership and transfer. The manifest subject points at buildings.

# $defs.Building.allOf[].properties.timeZone.description
IANA tz identifier. A fixed offset is not acceptable.

# $defs.Space.description
A bounded region. Recursive: sites contain buildings' spaces, storeys contain rooms. Nesting is expressed with bus:contains.

# $defs.Space.allOf[].properties.ordinal.description
Signed storey index; 0 is the principal ground storey. Applies where spaceKind is storey.

# $defs.Zone.description
A set of spaces that behave as one for some purpose. A zone is not a region and has no boundary.

# $defs.AssetType.description
A product type shared by many asset instances. Carries what is true of the model rather than the unit.

# $defs.Asset.description
A physical or virtual component that exists independently of any software platform.

# $defs.Asset.allOf[].properties.assetKind.description
equipment: a functional unit reasoned about as a whole. component: a separately maintained part. device: a thing that hosts points. virtual: exists only in software.

# $defs.Point.allOf[].properties.quantityKind.description
Reference to a bus:PropertyDefinition describing what is measured. Replaces the free token of v0.1.

# $defs.TelemetryBinding.description
How a point is reached in the live system. Preserved verbatim; never normalized.

# $defs.Predicate.description
The normative predicate set of BUS-1 v0.2.

# $defs.Relationship.description
A first-class, addressable, typed link. Both endpoints are intrinsic to it.

# $defs.Relationship.allOf[].properties.subjectPort.description
Placeholder pending the port model. See open issue H-1.

# $defs.Constraint.description
A limit that holds regardless of objectives. Distinct from Target: missing a target is a complaint, violating a constraint is a hazard.

# $defs.Sequence.description
The logic that implements an intent. Connected to intent by bus:implements. Not part of intent.

# $defs.Sequence.allOf[].properties.source.description
Inline sequence source where the language permits it and the size is reasonable.

# $defs.AlarmDefinition.description
The durable definition of an alarm condition and how it is to be handled. Attached to its subject by bus:appliesTo.

# $defs.AlarmDefinition.allOf[].properties.priority.description
Source system priority, preserved verbatim.

# $defs.Event.description
A timestamped occurrence. Not a time-series sample. The subject is intrinsic: an event without a subject is meaningless.

# $defs.CoordinateSystem.properties.unitCode.description
Length unit for drawing coordinates, e.g. m, mm, or ft.

# $defs.CoordinateSystem.properties.georeference.description
Anchors drawing coordinates to the real world. An anchored plan survives into any CAD, BIM or GIS tool indefinitely.

# $defs.CoordinateSystem.properties.georeference.properties.rotation.description
Degrees clockwise from true north to drawing +y.

# $defs.CoordinateSystem.properties.georeference.properties.crs.description
Coordinate reference system identifier, e.g. EPSG:4326.

# $defs.Drawing.description
A page of portable presentation: a floor plan, equipment graphic, schematic, or one-line.

# $defs.Drawing.allOf[].properties.referenceDimension.description
A known real-world distance between two drawing coordinates, so that a scale error is detectable rather than silent.

# $defs.Layer.allOf[].properties.purpose.description
Declared so a receiver can drop the architecture and keep the semantics.

# $defs.SymbolRole.description
A hierarchical dotted path naming what an element depicts. Degrades: fan.centrifugal.supply to fan.centrifugal to fan.

# $defs.Geometry.properties.coordinates.description
Flat array of alternating x and y values in drawing units.

# $defs.Element.description
A placed thing on a drawing. Carries a symbol role for the receiver to style, an embedded figure to be rendered as given, or both.

# $defs.Element.allOf[].properties.figure.description
Neutral vector artwork the receiver MUST render substantially as given. Used where the owner funded the artwork itself.

# $defs.Element.allOf[].properties.represents.description
The building entity this element depicts. Intrinsic: a symbol exists in order to depict something.

# $defs.Element.allOf[].properties.navigatesTo.description
Drawing this element opens when activated.

# $defs.BindingChannel.description
What aspect of an element a value drives. Closed vocabulary; extended only by a MINOR version.

# $defs.Binding.description
Drives an element from a building entity, or writes to one. Both endpoints are intrinsic; no bindsTo relationship is created.

# $defs.Binding.allOf[].properties.mapping.properties.states.items.properties.select.description
Named element state the receiver selects.

# $defs.Binding.allOf[].properties.mapping.properties.format.description
Numeric or text presentation hint, e.g. '0.0'.

# $defs.Binding.allOf[].properties.quality.description
Engineered behavior when the value is stale or unavailable. Not styling.

# $defs.Binding.allOf[].properties.write.description
Present when direction is write or readWrite. Carries actuation semantics that MUST NOT be substituted.

# $defs.Binding.allOf[].properties.write.properties.priority.description
Source command priority, preserved verbatim. A receiver that cannot honor it MUST report rather than substitute.

# $defs.Binding.allOf[].properties.write.properties.constraintRef.description
Permitted range. References a bus:Constraint rather than duplicating limits.