IFC 4.3.x development

8.11.3.4 IfcDerivedUnit

8.11.3.4.1 Semantic definitions at the entity

NOTE  Definition according to ISO/CD 10303-41:1992
A derived unit is an expression of units.

EXAMPLE  Newton per square millimetre is a derived unit.

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

HISTORY  New entity in IFC1.5.1.

8.11.3.4.1 Attributes

# Attribute Type Description
IfcDerivedUnit
1 Elements SET [1:?] OF IfcDerivedUnitElementThe group of units and their exponents that define the derived unit.
2 UnitType IfcDerivedUnitEnum Name of the derived unit chosen from an enumeration of derived unit types for use in IFC models.
3 UserDefinedTypeOPTIONAL IfcLabel
Dimensions INVALID Dimensional exponents derived using the function IfcDerivedDimensionalExponents using (SELF) as the input value.

8.11.3.4.2 Entity inheritance

dot_inheritance IfcDerivedUnit IfcDerivedUnit

8.11.3.4.3 Formal representations

ENTITY IfcDerivedUnit;
	Elements : SET [1:?] OF IfcDerivedUnitElement;
	UnitType : IfcDerivedUnitEnum;
	UserDefinedType : OPTIONAL IfcLabel;
 DERIVE
	 Dimensions : IfcDimensionalExponents := IfcDeriveDimensionalExponents(Elements);
 WHERE
	WR1 : (SIZEOF (Elements) > 1) OR ((SIZEOF (Elements) = 1) AND (Elements[1].Exponent <> 1 ));
	WR2 : (UnitType <> IfcDerivedUnitEnum.USERDEFINED) OR
((UnitType = IfcDerivedUnitEnum.USERDEFINED) AND 
 (EXISTS(SELF.UserDefinedType)));
END_ENTITY;