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partof-facet.md

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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 Allowed Values 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.
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)

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"