# Ontology Versioning¶

Brick models (digital representations of buildings) are often developed against a specific version of the Brick ontology. As the Brick ontology evolves, it is important to keep track of which version of the Brick ontology is required for a particular model.

This is accomplished through use of of (a) ontology declarations, and (b) ontology imports.

All Brick models should explicitly declare the graph which contains the statements modeling the building. An ontology declaration is a triple of the form:

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

<graph name> rdf:type owl:Ontology .


<graph name> is an RDF IRI, and is usually the same as the namespace that is used to define the entities in the building:

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix brick: <https://brickschema.org/schema/Brick#> .
@prefix bldg: <urn:my_building#> .

<urn:my_building> a owl:Ontology .


Since v1.2, all versions of the Brick ontology have the same namespace: https://brickschema.org/schema/Brick#. This makes it easier to upgrade the Brick ontology used with a particular model without having to change all of the classes, relationships, etc used by that model to use a different namespace. Instead, we use ontology imports to track the dependency on a particular version of Brick.

Ontology imports are properties of the owl:Ontology entity which point to other graphs via the owl:imports relationship.

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix brick: <https://brickschema.org/schema/Brick#> .
@prefix bldg: <urn:my_building#> .

<urn:my_building> a owl:Ontology ;
owl:imports <https://brickschema.org/schema/1.2/Brick#> .


The IRI of the imported graph has the version of the Brick ontology embedded in it. This versioned IRI points to the version of the Brick ontology indicated in the IRI; for example, https://brickschema.org/schema/1.2/Brick is v1.2 of Brick, https://brickschema.org/schema/1.3/Brick is v1.3 of Brick, and so on. To update Brick, it is only necessary to change the object of the owl:imports statement. This is possible because the IRI that imports Brick will always resolve to a file that uses the version-agnostic Brick namespace https://brickschema.org/schema/Brick#.