PartOf facet

This facet either identifies objects that are part-of another (applicability), or require that they are (requirement).

While objects in IFC can have multiple relationships to other objects. IDS part-of recursively navigates the following types to determine if an entity is part-of another:

The IFCRELAGGREGATES relationship describes how multiple smaller sub-objects can be aggregated into a single bigger object. For example, many building storeys make up a building. Alternatively, many beams, floor boards, and joints make up a slab. Or perhaps many brackets, mullions, and steel plates make up an assembly.
The IFCRELASSIGNSTOGROUP relationship describes how multiple objects can be grouped into a collection of objects any use-case. For example, ducts, AHUs, fans, and louvres may all be grouped into a single distribution system. Alternatively, cables, distribution boards, and GPOs may be grouped into a single circuit. Or perhaps spaces are grouped into zones, or maintainable assets are grouped into an inventory.
The IFCRELCONTAINEDINSPATIALSTRUCTURE relationship describes how multiple objects can be located in a particular location. For example, a pump might be in a space, a column might be on the level 2 building storey, or some street furniture might be on the building site. Every object must have a single primary location container in IFC, even though they may be referenced in multiple locations (such as a multi-storey column). This relationship only targets the primary location container.
The IFCRELNESTS relationship describes how a physical object may be connected to a larger host object, typically through a physical connection such as a pre-drilled hole or connection terminal. When the host moves, the attached nested objects move with it.
The IFCRELVOIDSELEMENT relationship describes how a void belongs to an element.
The IFCRELFILLSELEMENT relationship describes how an element fills a void, making it part of the void.

When the relation parameter is not specified, then all 6 are to be considered (recursively) to identify containing entities, otherwise only the specified relation type should be considered (also recursively).

Example of part of identification

Parameters

Parameter	Required	Type	Meaning
Entity	✔️	An entity facet	Any valid IDS `entityType`, nested in the XML (e.g. "IFCSYSTEM"). The IFC class of the larger object matches the required entity. Expressed in UPPERCASE.
Relation	❌	string	One relationship chosen from the 6 supported types listed above. If omitted any valid IFC relationship structure that directly or indirectly, and transitively (recursively) has to be evaluated, if specified only the given type must be evaluated (recursively). Expressed in UPPERCASE.

'Part Of' facet interpretation

Applicability

PartOf Entity	PartOf Relation*	IDS Interpretation
IFCSPACE	-	Applies to all objects being a part of an IfcSpace.
IFCSPACE	IFCRELCONTAINEDINSPATIALSTRUCTURE	Applies to all objects contained within an IfcSpace, as defined by the IfcRelContainedInSpatialStructure relation.

Requirements

IDS Cardinality	PartOf Entity	PartOf Relation*	Configuration Allowed?	IDS Interpretation
REQUIRED	IFCSPACE	-	✅	Applicable objects must have a relation to the IfcSpace entity (traversing all valid relationships).
REQUIRED	IFCSPACE	IFCRELCONTAINEDINSPATIALSTRUCTURE	✅	Applicable objects must have the IfcRelContainedInSpatialStructure relation to the IfcSpace entity.
OPTIONAL	IFCSPACE	-	❌	Not allowed. No added value in specifying that it can be a part or not.
OPTIONAL	IFCSPACE	IFCRELCONTAINEDINSPATIALSTRUCTURE	❌	Not allowed. No added value in specifying that it can be a part or not.
PROHIBITED	IFCSPACE	-	✅	Applicable objects must not have any relation to IfcSpace associated.
PROHIBITED	IFCSPACE	IFCRELCONTAINEDINSPATIALSTRUCTURE	✅	Applicable objects must not have the IfcRelContainedInSpatialStructure relation to IfcSpace associated.

* the field is an XML attribute

Examples

Applicability Intention	Requirement Intention	Facet Definition
Any entity that is directly composing a curtain wall	The entity (e.g. mullion) must be part of a curtain wall	Relation="IFCRELAGGREGATES", Entity="IFCCURTAINWALL"
Any entity that is directly or indirectly part of a curtain wall	The entity (e.g. mullion) must be part of a curtain wall	Entity="IFCCURTAINWALL"
Any entity that is part of a distribution system	The entity (e.g. duct) must be part of a distribution system	Relation="IFCRELASSIGNSTOGROUP", Entity="IFCDISTRIBUTIONSYSTEM"
Any entity that is located in a space	The entity (e.g. pump) must be located in a space	Relation="IFCRELCONTAINEDINSPATIALSTRUCTURE", Entity="IFCSPACE"
Any entity that is hosted by a wall	The entity (e.g. window) must be fixed on a wall	Relation="IFCRELNESTS", Entity="IFCWALL"