Aliases and Equivalent Classes

Note

This feature is new in Brick v1.4

Over its history, Brick has accumulated several duplicate class names. For example: brick:AHU, brick:Air_Handler_Unit and brick:Air_Handling_Unit can all be found in the Brick 1.4 release. Brick retains all of these classes for backwards-compatibility; however, in Brick 1.4 it became necessary to denote a preferred class among a set of interchangeable classes. At the same time, downstream tools and consumers should remain agnostic to whichever class was chosen by a modeler. Brick 1.4 handles both of these features through two mechanisms: equivalent classes and aliases.

Aliases

Aliases identify the preferred class among a set of interchangeable (equivalent) classes. Non-preferred classes will have a brick:aliasOf property which indicates the preferred class.

See below a snippet of Brick 1.4 containing definitions of AHU, Air_Handler_Unit and Air_Handling_Unit. Only brick:Air_Handling_Unit is missing the brick:aliasOf property, so it is the preferred class. The other classes have a brick:aliasOf property pointing to this preferred class.

brick:AHU a owl:Class, sh:NodeShape ;
    rdfs:label "AHU" ;
    owl:equivalentClass brick:Air_Handling_Unit ;
    brick:aliasOf brick:Air_Handling_Unit .

brick:Air_Handler_Unit a owl:Class, sh:NodeShape ;
    rdfs:label "Air Handler Unit" ;
    owl:equivalentClass brick:Air_Handling_Unit ;
    brick:aliasOf brick:Air_Handling_Unit .

brick:Air_Handling_Unit a owl:Class, sh:NodeShape ;
    rdfs:label "Air Handling Unit" ;
    rdfs:subClassOf brick:HVAC_Equipment ;
    owl:equivalentClass brick:AHU,
        brick:Air_Handler_Unit ;
    brick:hasAssociatedTag tag:AHU,
        tag:Air,
        tag:Equipment,
        tag:Handler,
        tag:Handling,
        tag:Unit .

Listing all Preferred Classes

This SPARQL query lists all preferred classes in Brick:

PREFIX brick: <https://brickschema.org/schema/Brick#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?preferred WHERE {
    ?preferred a owl:Class ;
               rdfs:subClassOf* brick:Entity .
    FILTER NOT EXISTS { ?preferred brick:aliasOf ?alias }
}

Here is how to run this query on the latest Brick release:

from rdflib import Graph
brick = Graph()
brick.parse("https://github.com/BrickSchema/Brick/releases/download/nightly/Brick.ttl", format="ttl")
res = brick.query("""
PREFIX brick: <https://brickschema.org/schema/Brick#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?preferred WHERE {
    ?preferred a owl:Class ;
               rdfs:subClassOf* brick:Entity .
    FILTER NOT EXISTS { ?preferred brick:aliasOf ?alias }
}
LIMIT 10
""")
for row in res.bindings:
    print(row)

{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Entity')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Measurable')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Substance')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Quantity')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Collection')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Portfolio')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Electric_Vehicle_Charging_Hub')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Photovoltaic_Array')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Loop')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Air_Loop')}

Getting the Preferred Class for an Entity

This SPARQL query gets the preferred class for a specific Brick class:

PREFIX brick: <https://brickschema.org/schema/Brick#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?preferred WHERE {
    { ?class brick:aliasOf ?preferred }
    UNION
    {
        BIND ( ?class AS ?preferred )
        FILTER NOT EXISTS { ?class brick:aliasOf ?other }
    }
}

Here is how to run this query on the latest Brick release. Adjust the initBindings paramete to change which class you are querying the alias for.

from rdflib import Graph, BRICK
brick = Graph()
brick.parse("https://github.com/BrickSchema/Brick/releases/download/nightly/Brick.ttl", format="ttl")

query = """
PREFIX brick: <https://brickschema.org/schema/Brick#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?preferred WHERE {
    { ?class brick:aliasOf ?preferred }
    UNION
    {
        BIND ( ?class AS ?preferred )
        FILTER NOT EXISTS { ?class brick:aliasOf ?other }
    }
}"""

# try this query for an alias
res = brick.query(query, initBindings={"class": BRICK.AHU})
for row in res.bindings:
    print(row)

# try this query for a preferred calss
res = brick.query(query, initBindings={"class": BRICK.Air_Handling_Unit})
for row in res.bindings:
    print(row)

{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Air_Handling_Unit')}
{rdflib.term.Variable('preferred'): rdflib.term.URIRef('https://brickschema.org/schema/Brick#Air_Handling_Unit')}

Equivalent Classes

Groups of duplicate classes (e.g., AHU, Air_Handler_Unit and Air_Handling_Unit) will also be marked as equivalent classes using the owl:equivalentClass property. There are two SHACL rules in Brick (bsh:OWLEquivalentClassRule1 and bsh:OWLEquivalentClassRule2) which handle the semantics of equivalent classes: when SHACL inference is run on a Brick model, these rules will add all the equivalent classes to each entity.

For example, consider a simple Brick model with a single AHU instance:

@prefix brick: <https://brickschema.org/schema/Brick#> .
@prefix : <urn:bldg#> .

:myAHU a brick:AHU .

After SHACL inference, the model will contain:

@prefix brick: <https://brickschema.org/schema/Brick#> .
@prefix : <urn:bldg#> .

:myAHU a brick:AHU, brick:Air_Handler_Unit, brick:Air_Handling_Unit .

This means that after running SHACL inference, one can use the preferred Brick classes to find an entity. It is not necessary to know which (equivalent) class was used.