Assembly

Represent composition explicitly

Assembly records describe a parent item that owns, encloses, or is composed of child items. Annex A's IFC mapping allows ParentName and ChildNames to resolve to either product instances or type objects, represented in the spreadsheet as Component or Type context selected by SheetName.

The spreadsheet schema uses the plural ChildNames heading but does not define it as a foreign key or include it in the compound key, while the IFC mapping resolves a child to one product or type name. The issued workbook and validator should therefore determine whether an implementation accepts a delimited child list or normalizes relationships into separate rows.

AssemblyType adds the nature of the composition, such as fixed, optional, included, excluded, layered, patched, or mixed. These distinctions can describe a manufactured set, a layered construction, or another contract-defined composition that cannot be communicated by a flat asset list alone.

Know when Assembly adds value

Assembly is different from System and Connection. A System groups assets by shared function, while a Connection describes a logical upstream-to-downstream relationship. Assembly says that one managed item is made from or contains others. The project should use the worksheet only when that composition is required and useful to the receiver.

The COBie 2.4 publication says Assembly is not required for the U.S. facility and asset-management exchanges covered by its design and handover QC testing. It is tested when supplied and may still be required by a contract or another implementation. When used, every parent and child must exist, repeated relationships should be removed, and circular chains must be prevented.

Reviewing Revit composition before export

Revit nested families, groups, assemblies, curtain systems, and host relationships can provide candidate composition evidence, but they do not automatically represent the hierarchy an operator wants. Authoring convenience and facility-management structure are different concerns, so source rules should be agreed rather than inferred from every nesting relationship.

BIMRelay keeps generated Assembly references tied to the source workbook rows and can validate that each parent and child exists after regeneration. Model context helps reviewers decide which relationships are meaningful, while project-controlled rows can be retained even when they are not directly derived from Revit geometry.