Restrict Fraction to Volume in IfcMaterialConstituent

[jbrouwerdigibase]

Description

This pull request refines the definition of the Fraction attribute in the IfcMaterialConstituent entity. Previously, Fraction could represent volume or weight, leading to potential inconsistencies.

Change

Volume-Specific Fraction: The Fraction attribute now exclusively refers to the volume proportion of a material constituent within the overall material set. This aligns with the inherent nature of material constituents in construction, where volume is the primary concern.

Rationale

There's limited practical use for specifying weight ratios between components like concrete, insulation, or reinforcement steel. Weight becomes relevant after the volume is established. By focusing on volume, we ensure consistent and meaningful data exchange within BIM workflows.

Benefits

Enhances data clarity and consistency across BIM models. Eliminates ambiguity during IFC data interpretation.