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Definition from buildingSMART: The assignment relationship, IfcRelAssigns, is a generalization of "link" relationships among instances of IfcObject and its various 1st level subtypes. A link denotes the specific association through which one object (the client) applies the services of other objects (the suppliers), or through which one object may navigate to other objects.

The client is denoted as the relating object and is established at the level of the specific, instantiable subtypes of IfcRelAssigns. The suppliers are denoted as the related objects and they are established by the RelatedObjects attribute.

NOTE: The terms "client" and "supplier" are used in a general concept and do not imply any meaning for implementations of systems (like client-server).
EXAMPLE: A resource may receive information about its nature of representing real building products by establishing a link between IfcResource and IfcBuildingElement (subtype of IfcProduct) throught he assignment relationship IfcRelAssignsToResource. The resource is then the client that applies the services of other objects (here building elements) to express the particular view of elements to be consumed as a resource in a process.

The assignment relationship establishs a bi-directional relationship among the participating objects and does not imply any dependency. The subtypes of IfcRelAssigns establishes the particular semantic meaning of the assignment relationship.

HISTORY: New entity in IFC Release 2x.

EXPRESS specification:

ENTITY IfcRelAssigns
ABSTRACT SUPERTYPE OF (ONEOF(IfcRelAssignsToProcess, IfcRelAssignsToProduct, IfcRelAssignsToControl, IfcRelAssignsToResource, IfcRelAssignsToActor, IfcRelAssignsToGroup))
SUBTYPE OF ( IfcRelationship);
RelatedObjects  :  SET [1:?] OF IfcObjectDefinition;
RelatedObjectsType  :  OPTIONAL IfcObjectTypeEnum;
WR1  :  IfcCorrectObjectAssignment(RelatedObjectsType, RelatedObjects);

Attribute definitions:

RelatedObjects  :  Related objects, which are assigned to a single object. The type of the single (or relating) object is defined in the subtypes of IfcRelAssigns.
RelatedObjectsType  :  Particular type of the assignment relationship. It can constrain the applicable object types, used within the role of RelatedObjects.

Formal Propositions:

WR1  :  Rule checks whether the types of the assigned related objects comply with the contraint given by the RelatedObjectsType. The rule is important for constraint checks at subtypes of IfcRelAssigns or at subtypes of IfcObject, which refers to assignment relationships through the inverse HasAssignments relation.

Inheritance graph

ENTITY IfcRelAssigns;
GlobalId  :  IfcGloballyUniqueId;
OwnerHistory  :  IfcOwnerHistory;
Name  :  OPTIONAL IfcLabel;
Description  :  OPTIONAL IfcText;
ENTITY IfcRelationship;
ENTITY IfcRelAssigns;
RelatedObjects  :  SET [1:?] OF IfcObjectDefinition;
RelatedObjectsType  :  OPTIONAL IfcObjectTypeEnum;