5.4.3.21 IfcElementQuantity
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 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.
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). 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:
- 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, Only the last modification is stored - either as addition, deletion or modification. 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. The relationship between the IfcPropertySetDefinition and the IfcTypeObject is a direct relationship, not utilizing IfcRelDefinesByProperties, for maintaining compatibility with earlier releases of this standard. 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. 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. Inverse attribute renamed from PropertyDefinitionOf with upward compatibility for file-based exchange. |
|
| Click to show 9 hidden inherited attributes Click to hide 9 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. 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. |
5.4.3.21.4 Formal propositions
| Name | Description |
|---|---|
| UniqueQuantityNames |
Every individual IfcPhysicalQuantity within the set Quantities shall have a unique Name attribute value. New rule in IFC4 |
|
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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 Click to hide 2 inherited concepts | |||
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;