5.4.3.21 IfcElementQuantity

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5.4.3.21.1 Semantic definition

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.

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.

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

count measure
weight measure
length measure
area measure
volume measure
time measure

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

IfcElementQuantity.Name =
IfcElementQuantity.MethodOfMeasurement = 'BaseQuantities'
IfcElementQuantity.Quantities = SET of subtypes of IfcPhysicalSimpleQuantity with values for the Name attribute as published as part of this specification.

5.4.3.21.2 Entity inheritance

5.4.3.21.3 Attributes

#	Attribute	Type	Description
IfcRoot (4)
1	GlobalId	IfcGloballyUniqueId	Assignment of a globally unique identifier within the entire software world.
2	OwnerHistory	OPTIONAL IfcOwnerHistory	Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object, NOTE Only the last modification is stored - either as addition, deletion or modification. IFC4-CHANGE The attribute has been changed to be OPTIONAL.
3	Name	OPTIONAL IfcLabel	Optional name for use by the participating software systems or users. For some subtypes of IfcRoot the insertion of the Name attribute may be required. This would be enforced by a where rule.
4	Description	OPTIONAL IfcText	Optional description, provided for exchanging informative comments.
IfcPropertyDefinition (2)
	HasContext	SET [0:1] OF IfcRelDeclares FOR RelatedDefinitions	Reference to the relationship IfcRelDeclares and thus to the IfcProject or IfcProjectLibrary.
	HasAssociations	SET [0:?] OF IfcRelAssociates FOR RelatedObjects	Reference to the relationship IfcRelAssociates and thus to those externally defined concepts, like classifications, documents, or library information, which are associated to the property definition.
IfcPropertySetDefinition (3)
	DefinesType	SET [0:?] OF IfcTypeObject FOR HasPropertySets	The type object to which the property set is assigned. The property set acts as a shared property set to all occurrences of the type object. NOTE The relationship between the IfcPropertySetDefinition and the IfcTypeObject is a direct relationship, not utilizing IfcRelDefinesByProperties, for maintaining compatibility with earlier releases of this standard. IFC4-CHANGE The cardinality has been changed from 0:1 to 0:? with upward compatibility for file based exchange.
	IsDefinedBy	SET [0:?] OF IfcRelDefinesByTemplate FOR RelatedPropertySets	Relation to the property set template, via the objectified relationship IfcRelDefinesByTemplate, that, if given, provides the definition template for the property set or quantity set and its properties. IFC4-CHANGE New inverse relationship, change made with upward compatibility for file based exchange.
	DefinesOccurrence	SET [0:?] OF IfcRelDefinesByProperties FOR RelatingPropertyDefinition	Reference to the relation to one or many object occurrences that are characterized by the property set definition. A single property set can be assigned to multiple object occurrences using the objectified relationship IfcRefDefinesByProperties. IFC4-CHANGE Inverse attribute renamed from PropertyDefinitionOf with upward compatibility for file-based exchange.
Click to show 9 hidden inherited attributes
IfcElementQuantity (2)
5	MethodOfMeasurement	OPTIONAL IfcLabel	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
6	Quantities	SET [1:?] OF IfcPhysicalQuantity	The individual quantities for the element, can be a set of length, area, volume, weight or count based quantities.

Table 5.4.3.21.A

5.4.3.21.4 Formal propositions

Name	Description
UniqueQuantityNames	Every individual IfcPhysicalQuantity within the set Quantities shall have a unique Name attribute value. HISTORY New rule in IFC4
`IfcUniqueQuantityNames(Quantities)`

Table 5.4.3.21.B

5.4.3.21.5 Concept usage

Concept	Usage	Description
IfcRoot (2)
Revision Control	General	Ownership, history, and merge state is captured using IfcOwnerHistory.
Software Identity	General	IfcRoot assigns the globally unique ID. In addition it may provide for a name and a description about the concept.
Click to show 2 hidden inherited concepts

Table 5.4.3.21.C

5.4.3.21.6 Formal representation

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

5.4.3.21.7 References

IfcQuantitySet