External representations (Brick v1.4)

Open-FDD models Brick points with Brick’s ref schema so software can discover how each point maps to external systems (BACnet and timeseries storage) using:

  • ref:hasExternalReference
  • ref:BACnetReference
  • ref:TimeseriesReference

Open-FDD keeps legacy ofdd:* BACnet fields for compatibility, but ref:* is the preferred representation.

When ref triples appear in the TTL

Brick external references (ref:hasExternalReference, etc.) are materialized when the Brick section of the graph is rebuilt from Postgres and the graph is serialized (same path as sync_brick_from_db / TTL generation). They are not invented solely by BACnet discovery in memory: discovery updates BACnet RDF in the graph, while ref:BACnetReference / ref:TimeseriesReference under each point come from current point rows in the DB when that Brick sync runs.

You will see ref: in TTL (or in View full data model) after any of these:

  • CRUD or import on sites, equipment, or points (the API reserializes Brick to disk on those paths).
  • GET /data-model/ttl with save=true (default in many clients), POST /data-model/serialize, or Data model → Serialize to TTL in the UI.
  • The background graph sync on a timer: interval graph_sync_interval_min (platform config). In the React app this is edited on OpenFDD Config, not the Overview page. See Configuration → Platform keys.

So if you only ran BACnet discovery and are watching config/data_model.ttl on disk, ref: may lag until the next serialize (timer or explicit action above). Discovery may also request a TTL write when write to file is enabled on that flow—otherwise rely on CRUD/import or an explicit serialize.

What Open-FDD emits

For each point in config/data_model.ttl:

  • A timeseries reference:
    • a ref:TimeseriesReference
    • ref:hasTimeseriesId "<external_id>"
    • ref:storedAt "<postgresql://host:port/db/timeseries_readings>"
  • A BACnet reference when BACnet addressing is known (bacnet_device_id + object_identifier):
    • a ref:BACnetReference
    • bacnet:object-identifier "<object-type,instance>"
    • optional bacnet:object-name "<name>"
    • bacnet:objectOf <bacnet://<device_instance>>
    • brick:BACnetURI "bacnet://<device>/<object>/present-value"

Example 

:pt_123 a brick:Zone_Air_Temperature_Sensor ;
    rdfs:label "ZoneTemp" ;
    ref:hasExternalReference [
        a ref:BACnetReference ;
        bacnet:object-identifier "analog-input,3" ;
        bacnet:object-name "BLDG-Z410-ZATS" ;
        brick:BACnetURI "bacnet://123/analog-input,3/present-value" ;
        bacnet:objectOf <bacnet://123>
    ] ;
    ref:hasExternalReference [
        a ref:TimeseriesReference ;
        ref:hasTimeseriesId "ZoneTemp" ;
        ref:storedAt "postgresql://localhost:5432/openfdd/timeseries_readings"
    ] ;
    brick:isPointOf :eq_ahu_1 .

SPARQL discovery pattern

Use this to enumerate all external references and their types:

PREFIX ref: <https://brickschema.org/schema/Brick/ref#>
SELECT ?point ?rep ?type WHERE {
  ?point ref:hasExternalReference ?rep .
  ?rep a ?type .
}

BACnet-only references:

PREFIX ref: <https://brickschema.org/schema/Brick/ref#>
PREFIX bacnet: <http://data.ashrae.org/bacnet/2020#>
SELECT ?point ?oid ?dev WHERE {
  ?point ref:hasExternalReference ?rep .
  ?rep a ref:BACnetReference ;
       bacnet:object-identifier ?oid ;
       bacnet:objectOf ?dev .
}

Timeseries-only references:

PREFIX ref: <https://brickschema.org/schema/Brick/ref#>
SELECT ?point ?tsid ?store WHERE {
  ?point ref:hasExternalReference ?rep .
  ?rep a ref:TimeseriesReference ;
       ref:hasTimeseriesId ?tsid ;
       ref:storedAt ?store .
}