IFC 4.3.x development

8.11.3.10 IfcSIUnit

8.11.3.10.1 Semantic definitions at the entity

The IfcSIUnit covers both standard base SI units such as meter and second, and derived SI units such as Pascal, square meter and cubic meter.

NOTE  Definition according to ISO/CD 10303-41:1992
An SI unit is the fixed quantity used as a standard in terms of which items are measured as defined by ISO 1000 (clause 2).

NOTE  Corresponding ISO 10303 name: si_unit, please refer to ISO/IS 10303-41 for the final definition of the formal standard.

HISTORY  New entity in IFC1.5.1.

8.11.3.10.1 Attributes

#Attribute Type Description
IfcNamedUnit
1Dimensions IfcDimensionalExponentsThe dimensional exponents of the SI base units by which the named unit is defined.
2UnitType IfcUnitEnum The type of the unit.
IfcSIUnit
3Prefix OPTIONAL IfcSIPrefix The SI Prefix for defining decimal multiples and submultiples of the unit.
4Name IfcSIUnitName The word, or group of words, by which the SI unit is referred to.

> NOTE  Even though the SI system's base unit for mass is kilogram, the IfcSIUnit for mass is gram if no Prefix is asserted.
1Dimensions INVALID The dimensional exponents of SI units are derived by function IfcDimensionsForSiUnit.

8.11.3.10.2 Entity inheritance

dot_inheritance IfcSIUnit IfcSIUnit IfcNamedUnit IfcNamedUnit IfcSIUnit->IfcNamedUnit IfcContextDependentUnit IfcContextDependentUnit IfcContextDependentUnit->IfcNamedUnit IfcConversionBasedUnit IfcConversionBasedUnit IfcConversionBasedUnit->IfcNamedUnit

8.11.3.10.3 Formal representations

ENTITY IfcSIUnit
 SUBTYPE OF (IfcNamedUnit);
	Prefix : OPTIONAL IfcSIPrefix;
	Name : IfcSIUnitName;
 DERIVE
	 SELF\IfcNamedUnit.Dimensions : IfcDimensionalExponents := IfcDimensionsForSiUnit (SELF.Name);
END_ENTITY;