IfcPropertySingleValue

IfcPropertySingleValue

实体定义

具有单个值的属性IfcPropertySingleValue定义了一个指定了单个（数字或描述性）值的属性对象。它定义了一个属性-单值组合，其中提供了属性名称、可选描述和可选的NominalValue以及度量值类型。此外，可以通过指定单位来覆盖项目单位上下文中指定的默认单位。

单位由单位属性处理，各种单值属性示例见表：

1、如果未给出Unit属性，则该单位已由IfcMeasureValue或IfcDerivedMeasureValue类型暗示。可以在项目级别全局定义的IfcUnitAssignment（IfcProject.UnitsContext）中找到关联的单元。

2、如果给定了单位属性，则单位属性指定的单位将覆盖全局指定的单位。

IFC1中增加的新实体

IFC2x更改实体已从IfcSimpleProperty重命名。

IFC2x3更改属性NominalValue已被设置为可选，并与基于文件的交换具有向上兼容性。

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcPropertyAbstraction
	HasExternalReferences	IfcExternalReferenceRelationship @RelatedResourceObjects	S[0:?]	Reference to an external reference, e.g. library, classification, or document information, that is associated to the property definition.	X
IfcProperty
1	Name	IfcIdentifier	[1:1]	Name for this property. This label is the significant name string that defines the semantic meaning for the property.	X
2	Description	IfcText	[0:1]	Informative text to explain the property.	X
	PartOfPset	IfcPropertySet @HasProperties	S[0:?]	Reference to the IfcPropertySet by which the IfcProperty is referenced.	X
	PropertyForDependance	IfcPropertyDependencyRelationship @DependingProperty	S[0:?]	The property on whose value that of another property depends.	X
	PropertyDependsOn	IfcPropertyDependencyRelationship @DependantProperty	S[0:?]	The relating property on which the value of the property depends.	X
	PartOfComplex	IfcComplexProperty @HasProperties	S[0:?]	Reference to the IfcComplexProperty in which the IfcProperty is contained.	X
	HasConstraints	IfcResourceConstraintRelationship @RelatedResourceObjects	S[0:?]	User-defined constraints for the property.	X
	HasApprovals	IfcResourceApprovalRelationship @RelatedResourceObjects	S[0:?]	User-defined approvals for the property.	X
IfcSimpleProperty
IfcPropertySingleValue
3	NominalValue	IfcValue	[0:1]	Value and measure type of this property. NOTE  By virtue of the defined data type, that is selected from the SELECT IfcValue, the appropriate unit can be found within the IfcUnitAssignment, defined for the project if no value for the unit attribute is given.	X
4	Unit	IfcUnit	[0:1]	Unit for the nominal value, if not given, the default value for the measure type (given by the TYPE of nominal value) is used as defined by the global unit assignment at IfcProject.	X

 

EXPRESS Specification

ENTITY IfcPropertySingleValue
 SUBTYPE OF (IfcSimpleProperty);
  NominalValue : OPTIONAL IfcValue;
  Unit : OPTIONAL IfcUnit;
END_ENTITY;

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