IfcSIUnit

BACnet MVD

#### 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

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
3 | Prefix | IfcSIPrefix | ? | The SI Prefix for defining decimal multiples and submultiples of the unit. |  | X

4

Name

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.

X

| Dimensions :=IfcDimensionsForSiUnit (SELF.Name) | IfcDimensionalExponents |  | The dimensional exponents of SI units are derived by function IfcDimensionsForSiUnit. |  | X

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
IfcNamedUnit
2 | UnitType | IfcUnitEnum |  | The type of the unit. |  | X
IfcSIUnit
3 | Prefix | IfcSIPrefix | ? | The SI Prefix for defining decimal multiples and submultiples of the unit. |  | X

4

Name

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.

X

| Dimensions :=IfcDimensionsForSiUnit (SELF.Name) | IfcDimensionalExponents |  | The dimensional exponents of SI units are derived by function IfcDimensionsForSiUnit. |  | X

##### Examples

- Basic unit declaration

##### Formal representations

XML 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

`

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