IfcDerivedUnit

Semantic definitions at the entity

Entity definition

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.

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
1	Elements	IfcDerivedUnitElement	S[1:?]	The group of units and their exponents that define the derived unit.	X
2	UnitType	IfcDerivedUnitEnum	[1:1]	Name of the derived unit chosen from an enumeration of derived unit types for use in IFC models.	X
3	UserDefinedType	IfcLabel	[0:1]		X
	Dimensions :=IfcDeriveDimensionalExponents(Elements)	IfcDimensionalExponents	[1:1]	Dimensional exponents derived using the function IfcDerivedDimensionalExponents using (SELF) as the input value.	X

Formal Propositions

Rule	Description
WR1	Units as such shall not be re-defined as derived units.
WR2	When attribute UnitType has enumeration value USERDEFINED then attribute UserDefinedType shall also have a value.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcDerivedUnit
1	Elements	IfcDerivedUnitElement	S[1:?]	The group of units and their exponents that define the derived unit.	X
2	UnitType	IfcDerivedUnitEnum	[1:1]	Name of the derived unit chosen from an enumeration of derived unit types for use in IFC models.	X
3	UserDefinedType	IfcLabel	[0:1]		X
	Dimensions :=IfcDeriveDimensionalExponents(Elements)	IfcDimensionalExponents	[1:1]	Dimensional exponents derived using the function IfcDerivedDimensionalExponents using (SELF) as the input value.	X

Formal representations

XSD Specification

 <xs:element name="IfcDerivedUnit" type="ifc:IfcDerivedUnit" substitutionGroup="ifc:Entity" nillable="true"/>

 <xs:complexType name="IfcDerivedUnit">

  <xs:complexContent>

   <xs:extension base="ifc:Entity">

    <xs:sequence>

     <xs:element name="Elements">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcDerivedUnitElement" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcDerivedUnitElement"/>

       <xs:attribute ref="ifc:cType" fixed="set"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

    </xs:sequence>

    <xs:attribute name="UnitType" type="ifc:IfcDerivedUnitEnum" use="optional"/>

    <xs:attribute name="UserDefinedType" type="ifc:IfcLabel" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


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;

 EXPRESS-G diagram

	Abgeleitete Einheit
	Derived Unit
	Unité dérivée