﻿ IfcSIUnit

#### IfcSIUnit

Natural language names
 SI Einheit SIUnit Unité du système international
##### Semantic definitions at the entity
Entity definition

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.
Attribute definitions
#AttributeTypeCardinalityDescription C
3PrefixIfcSIPrefix[0:1] The SI Prefix for defining decimal multiples and submultiples of the unit.X
4NameIfcSIUnitName[1:1] 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.
X
Dimensions
:=IfcDimensionsForSiUnit (SELF.Name)
IfcDimensionalExponents[1:1]The dimensional exponents of SI units are derived by function IfcDimensionsForSiUnit. X
##### Inherited definitions from supertypes
Entity inheritance
Attribute inheritance
#AttributeTypeCardinalityDescriptionC
IfcNamedUnit
2UnitTypeIfcUnitEnum[1:1] The type of the unit.X
IfcSIUnit
3PrefixIfcSIPrefix[0:1] The SI Prefix for defining decimal multiples and submultiples of the unit.X
4NameIfcSIUnitName[1:1] 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.
X
Dimensions
:=IfcDimensionsForSiUnit (SELF.Name)
IfcDimensionalExponents[1:1]The dimensional exponents of SI units are derived by function IfcDimensionsForSiUnit. X
##### Formal representations
XSD Specification
``` <xs:complexType name="IfcSIUnit-temp" abstract="true">   <xs:complexContent>    <xs:restriction base="ifc:IfcNamedUnit">     <xs:sequence/>    </xs:restriction>   </xs:complexContent>  </xs:complexType>  <xs:element name="IfcSIUnit" type="ifc:IfcSIUnit" substitutionGroup="ifc:IfcNamedUnit" nillable="true"/>  <xs:complexType name="IfcSIUnit">   <xs:complexContent>    <xs:extension base="ifc:IfcSIUnit-temp">     <xs:attribute name="Prefix" type="ifc:IfcSIPrefix" use="optional"/>     <xs:attribute name="Name" type="ifc:IfcSIUnitName" use="optional"/>    </xs:extension>   </xs:complexContent>  </xs:complexType> ```
EXPRESS Specification
``` ENTITY IfcSIUnit  SUBTYPE OF (IfcNamedUnit);   Prefix : OPTIONAL IfcSIPrefix;   Name : IfcSIUnitName;  DERIVE   SELF\IfcNamedUnit.Dimensions : IfcDimensionalExponents := IfcDimensionsForSiUnit (SELF.Name); END_ENTITY;  EXPRESS-G diagram ```