B Symbol role vocabulary, tier one§
Roles are hierarchical dotted paths in lowerCamelCase segments. A receiver truncates at successive dots until it reaches a role it implements. An implementation MUST support every root in this table; support for deeper leaves is RECOMMENDED and never required.
The tier holds fifty-two roots and seventy-five named leaves: small enough to ratify, large enough to cover the overwhelming majority of building graphics. The failure mode to avoid is a three-hundred-role taxonomy project that never ships, and the fallback rule is what makes that avoidable: an implementation that supports only the roots is conforming, and one that supports every leaf is better.
| Family | Root | Leaves and notes |
|---|---|---|
| Air movement | fan | fan.centrifugal, fan.axial, fan.plug; and by service fan.centrifugal.supply, .return, .exhaust, .relief |
damper | damper.modulating, damper.twoPosition, damper.fireSmoke; by service damper.modulating.outsideAir, .mixed, .bypass | |
louver | Fixed intake or discharge louver. | |
duct | duct.segment, duct.segment.supply, .return, .exhaust, .outsideAir | |
plenum, mixingBox | Air paths that are not ducts. | |
diffuser, grille | Terminal air devices. | |
terminal | terminal.vav, terminal.vav.reheat, terminal.cav, terminal.fanPowered | |
| Wet side | pump | pump.centrifugal, pump.inline; by service pump.centrifugal.chilledWater, .hotWater, .condenser |
valve | valve.twoWay, valve.threeWay, valve.modulating, valve.isolation, valve.check | |
coil | coil.cooling, coil.heating, coil.preheat, coil.reheat; by medium coil.cooling.chilledWater, coil.cooling.directExpansion | |
pipe | pipe.segment with the medium carried by the binding or the represented entity. | |
heatExchanger, tank, humidifier | Plant items that are neither a coil nor a vessel. | |
| Plant | chiller | chiller.centrifugal, chiller.screw, chiller.absorption, chiller.airCooled |
boiler | boiler.condensing, boiler.steam, boiler.electric | |
coolingTower | coolingTower.openCircuit, coolingTower.closedCircuit | |
compressor, filter | filter.panel, filter.bag, filter.hepa | |
| Electrical | breaker, switch, transformer, panel, busway, generator, ups, meter.electrical | One-line and riser primitives. |
| Controls | controller, actuator, vfd, relay, thermostat | Control devices shown on a graphic. |
sensor | sensor.temperature, sensor.pressure, sensor.flow, sensor.humidity, sensor.co2, sensor.occupancy, sensor.current | |
| Interface | readout.value, readout.text | Displayed values distinct from the thing that produces them. |
indicator.status, indicator.alarm | State annunciation. | |
gauge, trend, bar | Value presentation forms. | |
control.input.numeric, control.input.enum, control.button.toggle, control.button.momentary, control.slider | Interactive elements. A write binding attaches to one of these. | |
label.text, label.dimension, legend, navigation.link, group | Annotation and structure. | |
| Space | space.boundary, wall, door, window, core, stair, column | Architectural context on a plan. Usually geometry rather than symbol. |
NOTE Anything outside this vocabulary uses figure mode (13.4.3). An exporter SHOULD prefer a role where one fits, because a role is what lets the receiving vendor apply its own design system; a figure is rendered as given and therefore looks foreign in the receiving interface.