IfcExternalReference

IfcExternalReference

实体定义

IfcExternalReference是当前模型或项目数据库中未明确表示的信息的标识（作为当前模型的实现）。这些信息可以包含在分类、文档或库中。IfcExternalReference标识特定项，例如字典条目、分类符号或外部源中的文档引用。

仅给出位置（作为URL）来描述可以找到信息的位置。此外，还提供了一个可选标识作为键，以允许更具体的引用（如节或表）。标识定义了一种系统可解释的方法，用于在源处标识信息的相关部分。此外，可以指定一个人类可解释的名称来标识信息主题，例如分类代码。

IfcExternalReference是所有外部引用实体的抽象超类型。

IFC2x中的新实体。

IFC 2x4更改从ItemReference重命名的属性标识，更改属性位置数据类型，并添加反向属性ExternalReferenceForResources。

Formal Propositions

Rule	Description
WR1	One of the attributes of IfcExternalReference should have a value assigned.

 

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcExternalReference
1	Location	IfcURIReference	[0:1]	Location, where the external source (classification, document or library) can be accessed by electronic means. The electronic location is provided as an URI, and would normally be given as an URL location string.	X
2	Identification	IfcIdentifier	[0:1]	The Identification provides a unique identifier of the referenced item within the external source (classification, document or library). It may be provided as a key, e.g. a classification notation, like NF2.3 a handle a uuid or guid It may be human readable (such as a key) or not (such as a handle or uuid) depending on the context of its usage (which has to be determined by local agreement).	X
3	Name	IfcLabel	[0:1]	Optional name to further specify the reference. It can provide a human readable identifier (which does not necessarily need to have a counterpart in the internal structure of the document).	X
	ExternalReferenceForResources	IfcExternalReferenceRelationship @RelatingReference	S[0:?]	Reference to all associations between this external reference and objects within the IfcResourceObjectSelect that are tagged by the external reference.	X

 

EXPRESS Specification

ENTITY IfcExternalReference
 ABSTRACT SUPERTYPE OF(ONEOF(IfcClassificationReference, IfcDocumentReference, IfcExternallyDefinedHatchStyle, IfcExternallyDefinedSurfaceStyle, IfcExternallyDefinedTextFont, IfcLibraryReference));
  Location : OPTIONAL IfcURIReference;
  Identification : OPTIONAL IfcIdentifier;
  Name : OPTIONAL IfcLabel;
 INVERSE
  ExternalReferenceForResources : SET [0:?] OF IfcExternalReferenceRelationship FOR RelatingReference;
 WHERE
  WR1 : EXISTS(Identification) OR EXISTS(Location) OR EXISTS(Name);
END_ENTITY;

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