8.11.3.4 IfcDerivedUnit
8.11.3.4.1 Semantic definition
A derived unit is a unit that is formed from an expression of other units.
Figure 8.11.3.4.A — An example of how to assign miles per hour as a derived unit
8.11.3.4.2 Entity inheritance
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8.11.3.4.3 Attributes
| # |
Attribute |
Type |
Description |
|
IfcDerivedUnit
(5)
|
| 1 |
Elements
|
SET [1:?] OF IfcDerivedUnitElement |
The group of units and their exponents that define the derived unit.
|
| 2 |
UnitType
|
IfcDerivedUnitEnum |
Type of the derived unit chosen from an enumeration of derived unit types for use in IFC models.
|
| 3 |
UserDefinedType
|
OPTIONAL IfcLabel |
Type of the derived unit if the UnitType attribute is set to USERDEFINED.
|
| 4 |
Name
|
OPTIONAL IfcLabel |
Name of the unit in addition to the unit type, particularly when the derived unit elements refer to conversion or context based units.
|
| * |
Dimensions
|
IfcDimensionalExponents |
This attribute is formally derived.
IfcDeriveDimensionalExponents(Elements)
Dimensional exponents derived using the function IfcDerivedDimensionalExponents using (SELF) as the input value.
|
Table 8.11.3.4.B
8.11.3.4.4 Formal propositions
| Name |
Description |
| WR1 |
Units as such shall not be re-defined as derived units.
|
(SIZEOF (Elements) > 1) OR ((SIZEOF (Elements) = 1) AND (Elements[1].Exponent <> 1 ))
|
| WR2 |
When attribute UnitType has enumeration value USERDEFINED
then attribute UserDefinedType shall also have a value.
|
(UnitType <> IfcDerivedUnitEnum.USERDEFINED) OR
((UnitType = IfcDerivedUnitEnum.USERDEFINED) AND
(EXISTS(SELF.UserDefinedType)))
|
Table 8.11.3.4.C
8.11.3.4.5 Formal representation
ENTITY IfcDerivedUnit;
Elements : SET [1:?] OF IfcDerivedUnitElement;
UnitType : IfcDerivedUnitEnum;
UserDefinedType : OPTIONAL IfcLabel;
Name : 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;
8.11.3.4.6 References