#### 8.9.3.6 IfcSIUnit

| Unité du système international
| SI Einheit

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.

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;

Attribute Definitions:

Prefix | : | The SI Prefix for defining decimal multiples and submultiples of the unit.
Name | : | 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.
Dimensions | : | The dimensional exponents of SI units are derived by function IfcDimensionsForSiUnit.

Inheritance Graph:

ENTITY IfcSIUnit

| ENTITY IfcNamedUnit

UnitType | : | IfcUnitEnum;

| ENTITY IfcSIUnit

Prefix | : | OPTIONAL IfcSIPrefix;
Name | : | IfcSIUnitName;

| DERIVE

Dimensions | : | IfcDimensionalExponents := IfcDimensionsForSiUnit (SELF.Name);

END_ENTITY;

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