http://www.buildingsmart-tech.org/ifc/IFC4/Add2/html/link/ifcshapeaspect.htm
The description for the attribute “ProductDefinitional” doesn’t really make sense to me.
Could this be improved? In particular the reference to a cantilever. Perhaps a window example might be more relevant.
An indication that the shape aspect is on the physical boundary of the product definition shape. If the value of this attribute is TRUE, it shall be asserted that the shape aspect being identified is on such a boundary. If the value is FALSE, it shall be asserted that the shape aspect being identified is not on such a boundary. If the value is UNKNOWN, it shall be asserted that it is not known whether or not the shape aspect being identified is on such a boundary. — EXAMPLE: Would be FALSE for a center line, identified as shape aspect; would be TRUE for a cantilever. —