Quantité d'élément
frei definierbare Elementmengenliste

An IfcElementQuantity defines a set of derived measures of an element's physical property. Elements could be spatial structure elements (like buildings, storeys, or spaces) or building elements (like walls, slabs, finishes). The IfcElementQuantity gets assigned to the element by using the IfcRelDefinesByProperties relationship.

The optional MethodOfMeasurement attribute defines the code, e.g. from a standard method of measurement, which had been used to calculate the element quantity.

NOTE  The recognizable values for the name and the method of measurement attributes have to be agreed upon in further agreement documents, such as implementers agreements. Some of these agreements might be limited to a certain region, to which the method of measurement applies.

The name attribute, given at the individual Quantities provides a recognizable semantic meaning of the element quantity. Both information is needed to establish a precise meaning for the measure value. An optional description may be assigned to each of the Quantities. All quantities assigned by a single instance of IfcElementQuantity are deemed to have been generated according to the same method of measurement. However several instances of IfcElementQuantity are assignable to an element, thus allowing for an element having quantities generated according to several methods of measurement.

EXAMPLE  To exchange the net floor area of spaces in the German region (as IfcSpace), the name might be 'Netto-Grundfläche' (net floor area), and the method of measurement might be accordingly 'DIN277-2' (German industry norm no. 277 edition 2).
EXAMPLE  The same instance of IfcSpace may have a different area measure assigned in the German region according to a housing regulation, the name would be 'Wohnfläche' and the method of measurement would be '2.BV'. It would be attached to the IfcSpace by a separate IfcRelDefinesByProperties relationship.<

The IfcElementQuantity can have the following subtypes of IfcPhysicalQuantity within its SET of Quantities, which count for the basis measure types used:

HISTORY  New entity in IFC2x.
IFC4 CHANGE  Subtyped from new intermediateIfcQuantitySet supertype.

Quantity Use Defintion

Base quantities are quantity definitions that are independent of a particular method of measurement and therefore internationally applicable. Base quantities are defined as gross and net values and provided by measurement of the correct geometric shape representation of the element. This specification includes a set of base quantity definition. See each subtype of IfcElement for applicable base quantities.

The following general agreements apply for each base quantity set

XSD Specification:

 <xs:element name="IfcElementQuantity" type="ifc:IfcElementQuantity" substitutionGroup="ifc:IfcQuantitySet" nillable="true"/>
 <xs:complexType name="IfcElementQuantity">
   <xs:extension base="ifc:IfcQuantitySet">
     <xs:element name="Quantities">
        <xs:element ref="ifc:IfcPhysicalQuantity" maxOccurs="unbounded"/>
       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcPhysicalQuantity"/>
       <xs:attribute ref="ifc:cType" fixed="set"/>
       <xs:attribute ref="ifc:arraySize" use="optional"/>
    <xs:attribute name="MethodOfMeasurement" type="ifc:IfcLabel" use="optional"/>

EXPRESS Specification:

ENTITY IfcElementQuantity
SUBTYPE OF IfcQuantitySet;
MethodOfMeasurement : OPTIONAL IfcLabel;
Quantities : SET [1:?] OF IfcPhysicalQuantity;
UniqueQuantityNames : IfcUniqueQuantityNames(Quantities);

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

MethodOfMeasurement : Name of the method of measurement used to calculate the element quantity. The method of measurement attribute has to be made recognizable by further agreements.
IFC2x2 Addendum 1 change: The attribute has been changed to be optional
Quantities : The individual quantities for the element, can be a set of length, area, volume, weight or count based quantities.

Formal Propositions:

UniqueQuantityNames : Every individual IfcPhysicalQuantity within the set Quantities shall have a unique Name attribute value.
HISTORY  New rule in IFC4

Inheritance Graph:

ENTITY IfcElementQuantity
GlobalId : IfcGloballyUniqueId;
OwnerHistory : OPTIONAL IfcOwnerHistory;
Name : OPTIONAL IfcLabel;
Description : OPTIONAL IfcText;
ENTITY IfcPropertyDefinition
HasContext : SET [0:1] OF IfcRelDeclares FOR RelatedDefinitions;
HasAssociations : SET OF IfcRelAssociates FOR RelatedObjects;
ENTITY IfcPropertySetDefinition
DefinesType : SET OF IfcTypeObject FOR HasPropertySets;
IsDefinedBy : SET OF IfcRelDefinesByTemplate FOR RelatedPropertySets;
DefinesOccurrence : SET [0:1] OF IfcRelDefinesByProperties FOR RelatingPropertyDefinition;
ENTITY IfcQuantitySet
ENTITY IfcElementQuantity
MethodOfMeasurement : OPTIONAL IfcLabel;
Quantities : SET [1:?] OF IfcPhysicalQuantity;

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