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IfcObjectDefinition

Definition from IAI: An IfcObjectDefinition is the generalization of any semantically treated thing or process, either being a type or an occurrences. Object defintions can be named, using the inherited Name attribute, which should be a user recognizable label for the object occurrance. Further explanations to the object can be given using the inherited Description attribute. 

Objects are independent pieces of information that might contain or reference other pieces of information. There are three essential kinds of relationships in which object definitons (by their instantiable subtypes) can be involved:

HISTORY  New abstract entity in Release IFC2x Edition 3.
IFC2x Edition 3 CHANGE  The abstract entity IfcObjectDefinition has been added. Upward compatibility for file based exchange is guaranteed.

EXPRESS specification:

ENTITY IfcObjectDefinition
ABSTRACT SUPERTYPE OF (ONEOF(IfcObject, IfcTypeObject))
SUBTYPE OF ( IfcRoot);
INVERSE
HasAssignments  :  SET OF IfcRelAssigns FOR RelatedObjects;
IsDecomposedBy  :  SET OF IfcRelDecomposes FOR RelatingObject;
Decomposes  :  SET [0:1] OF IfcRelDecomposes FOR RelatedObjects;
HasAssociations  :  SET OF IfcRelAssociates FOR RelatedObjects;
END_ENTITY;

Attribute definitions:

HasAssignments  :  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.
IsDecomposedBy  :  Reference to the decomposition relationship, that allows this object to be the composition of other objects. An object can be decomposed by several other objects.
Decomposes  :  References to the decomposition relationship, that allows this object to be a part of the decomposition. An object can only be part of a single decomposition (to allow hierarchical strutures only).
HasAssociations  :  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.

Inheritance graph

ENTITY IfcObjectDefinition;
ENTITY IfcRoot;
GlobalId  :  IfcGloballyUniqueId;
OwnerHistory  :  IfcOwnerHistory;
Name  :  OPTIONAL IfcLabel;
Description  :  OPTIONAL IfcText;
ENTITY IfcObjectDefinition;
INVERSE
HasAssignments  :  SET OF IfcRelAssigns FOR RelatedObjects;
IsDecomposedBy  :  SET OF IfcRelDecomposes FOR RelatingObject;
Decomposes  :  SET [0:1] OF IfcRelDecomposes FOR RelatedObjects;
HasAssociations  :  SET OF IfcRelAssociates FOR RelatedObjects;
END_ENTITY;