Shared versus Private Properties

buildingSMART’s IFC, COBie, and other BIM applications, distinguish between Shared and Private properties as follows:

Shared	Defined by type as in shared or common values across multiple instances.
Private	Defined at the instance when unique property values for each instance of that type (1) add to the shared property values, or (2) redefine or override the shared property values.

Note: Property values redefined on the instance, override the property values defined by the type.

An instance can have (in order of strong to soft typing):

Only shared property values inherited from its type.
Shared property values inherited from its type, plus additional private property values.
Shared property values inherited from its type, some of which are redefined on the instance.
Shared property values inherited from it’s type, some of which are redefined on the instance, plus additional private property values.
Only private property values.

IFC Viewers, such as the FZK Viewer, may display shared properties as PropertySets from entity type and private properties as PropertySets from entity.

Note: PropertySets from entity type display all property values defined for the type (such as Frame | Material: STL for example) even if the properties are redefined in PropertySets from entity (such as Frame | Material: WD for example).