IfcObjectDefinition

IfcObjectDefinition是IFC2x3中增加的。

IFC4更改了新的子类型IfcContext，并且添加了与context HasContext的关系。分解关系分为有序嵌套（Nests，IsNestedBy）和非有序聚合（Decomposes，IsDecomposedBy）。

IfcObjectDefinition是任何经过语义处理的事物或过程的泛化，可以是类型，也可以是事件。可以使用继承的Name属性命名对象定义，该属性应该是对象发生时用户可识别的标签。可以使用继承的Description属性进一步解释对象。上下文是一种特定的对象定义，因为它提供了定义对象类型和对象引用的项目或库上下文。

对象是独立的信息片段，可能包含或引用其他信息片段。对象定义（按其可实例化的子类型）可以涉及四种基本关系：

其他对象的赋值-引用其他类型对象并创建双向关联的赋值关系（IfcRelAssigns）。赋值的语义是在一般ifcreassigns关系的子类型级别上建立的。赋值没有先验的依赖关系。

与外部资源的关联-一种关联关系（ifcreassociates），它引用外部信息源（尤其是分类或文档），并创建单向关联。关联不隐含依赖关系。

其他对象的聚合-建立无序的空间整体/部分关系并创建双向关系的聚合关系（IfcRelAggregates）。已建立隐含的依赖关系。

其他对象的嵌套-建立有序、非空间整体/部分关系并创建双向关系的嵌套关系（IfcRelNests）。已建立隐含的依赖关系。

上下文中的声明-对象定义树中最上面的对象定义（例如对象嵌套树中的摘要对象）与上下文（项目或项目库）的关系（IfcRelDeclares）。它将单位、表示上下文和其他上下文信息应用于此对象定义和所有相关的对象定义。

请注意空间结构树中最上面的对象（即IfcSite或ifcBuilding）与IfcProject提供的上下文之间的链接是使用ifcrelaggregegates关系创建的。有关详细信息，请参见IfcProject。

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
	HasAssignments	IfcRelAssigns @RelatedObjects	S[0:?]	Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.	X
	Nests	IfcRelNests @RelatedObjects	S[0:1]	References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only).	X
	IsNestedBy	IfcRelNests @RelatingObject	S[0:?]	References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types).	X
	HasContext	IfcRelDeclares @RelatedDefinitions	S[0:1]	References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object.	X
	IsDecomposedBy	IfcRelAggregates @RelatingObject	S[0:?]	References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts).	X
	Decomposes	IfcRelAggregates @RelatedObjects	S[0:1]	References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only).	X
	HasAssociations	IfcRelAssociates @RelatedObjects	S[0:?]	Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcRoot
1	GlobalId	IfcGloballyUniqueId	[1:1]	Assignment of a globally unique identifier within the entire software world.	X
2	OwnerHistory	IfcOwnerHistory	[0:1]	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 in stored - either as addition, deletion or modification.	X
3	Name	IfcLabel	[0:1]	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.	X
4	Description	IfcText	[0:1]	Optional description, provided for exchanging informative comments.	X
IfcObjectDefinition
	HasAssignments	IfcRelAssigns @RelatedObjects	S[0:?]	Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.	X
	Nests	IfcRelNests @RelatedObjects	S[0:1]	References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only).	X
	IsNestedBy	IfcRelNests @RelatingObject	S[0:?]	References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types).	X
	HasContext	IfcRelDeclares @RelatedDefinitions	S[0:1]	References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object.	X
	IsDecomposedBy	IfcRelAggregates @RelatingObject	S[0:?]	References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts).	X
	Decomposes	IfcRelAggregates @RelatedObjects	S[0:1]	References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only).	X
	HasAssociations	IfcRelAssociates @RelatedObjects	S[0:?]	Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification.	X