Modifikator (geometrischer Körper) - Subtraktion

The IfcFeatureElementSubtraction is specialization of the general feature element, that represents an existence dependent elements which modifies the shape and appearance of the associated master element. The IfcFeatureElementSubtraction offers the ability to handle shape modifiers as semantic objects within the IFC object model that subtract from the shape of the master element.

NOTE  A single subtraction feature such as the subtype IfcOpeningElement is assigned by a single subtraction relationship IfcRelVoidsElement to one occurrences of IfcElement. It establishes a 1:1 relationship between the opening and the element. An element may have several IfcRelVoidsElement relationships, enabling several voids.

The voiding relationship between a master element and a subtraction feature is geometrically resolved by a Boolean difference operation.

HISTORY  New entity in IFC2x2.
IFC2x2 CHANGE  The entity is introduced as an upward compatible extension of the IFC2x platform. It is an intermediate abstract supertype without defining its own explicit attributes.

Geometry Use Definitions

The geometric representation of IfcFeatureElementSubtraction is given by the IfcProductDefinitionShape, allowing multiple geometric representations.

Local Placement

The local placement for IfcFeatureElementSubtraction is defined in its supertype IfcProduct. It is defined by the IfcLocalPlacement, which defines the local coordinate system that is referenced by all geometric representations. The local placement is always defined in relation to the local placement of the building element from which the feature element substration is substracted:

Shape Representation

The geometry use definitions for the shape representation of the IfcFeatureElementSubtraction is given at the level of its subtypes.

XSD Specification:

 <xs:element name="IfcFeatureElementSubtraction" type="ifc:IfcFeatureElementSubtraction" abstract="true" substitutionGroup="ifc:IfcFeatureElement" nillable="true"/>
 <xs:complexType name="IfcFeatureElementSubtraction" abstract="true">
   <xs:extension base="ifc:IfcFeatureElement"/>

EXPRESS Specification:

ENTITY IfcFeatureElementSubtraction
ABSTRACT SUPERTYPE OF(ONEOF(IfcOpeningElement, IfcVoidingFeature))
SUBTYPE OF IfcFeatureElement;
VoidsElements : IfcRelVoidsElement FOR RelatedOpeningElement;
HasNoSubtraction : SIZEOF(SELF\IfcElement.HasOpenings) = 0;
IsNotFilling : SIZEOF(SELF\IfcElement.FillsVoids) = 0;

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

VoidsElements : Reference to the Voids Relationship that uses this Opening Element to create a void within an Element. The Opening Element can only be used to create a single void within a single Element.

Formal Propositions:

HasNoSubtraction : An feature subtraction (e.g. an opening element) can not have other openings to void itself. The inverse relationship HasOpenings shall therefore be NIL.
IsNotFilling : An feature subtraction (e.g. an opening element) can not be a filling of another void. The inverse relationship FillsVoids shall therefore be NIL.

Inheritance Graph:

ENTITY IfcFeatureElementSubtraction
GlobalId : IfcGloballyUniqueId;
OwnerHistory : OPTIONAL IfcOwnerHistory;
Name : OPTIONAL IfcLabel;
Description : OPTIONAL IfcText;
ENTITY IfcObjectDefinition
HasAssignments : SET OF IfcRelAssigns FOR RelatedObjects;
Nests : SET [0:1] OF IfcRelNests FOR RelatedObjects;
IsNestedBy : SET OF IfcRelNests FOR RelatingObject;
HasContext : SET [0:1] OF IfcRelDeclares FOR RelatedDefinitions;
IsDecomposedBy : SET OF IfcRelAggregates FOR RelatingObject;
Decomposes : SET [0:1] OF IfcRelAggregates FOR RelatedObjects;
HasAssociations : SET OF IfcRelAssociates FOR RelatedObjects;
ENTITY IfcObject
ObjectType : OPTIONAL IfcLabel;
IsDeclaredBy : SET [0:1] OF IfcRelDefinesByObject FOR RelatedObjects;
Declares : SET OF IfcRelDefinesByObject FOR RelatingObject;
IsTypedBy : SET [0:1] OF IfcRelDefinesByType FOR RelatedObjects;
IsDefinedBy : SET OF IfcRelDefinesByProperties FOR RelatedObjects;
ENTITY IfcProduct
ObjectPlacement : OPTIONAL IfcObjectPlacement;
Representation : OPTIONAL IfcProductRepresentation;
ReferencedBy : SET OF IfcRelAssignsToProduct FOR RelatingProduct;
ENTITY IfcElement
Tag : OPTIONAL IfcIdentifier;
FillsVoids : SET [0:1] OF IfcRelFillsElement FOR RelatedBuildingElement;
ConnectedTo : SET OF IfcRelConnectsElements FOR RelatingElement;
IsInterferedByElements : SET OF IfcRelInterferesElements FOR RelatedElement;
InterferesElements : SET OF IfcRelInterferesElements FOR RelatingElement;
HasProjections : SET OF IfcRelProjectsElement FOR RelatingElement;
ReferencedInStructures : SET OF IfcRelReferencedInSpatialStructure FOR RelatedElements;
HasOpenings : SET OF IfcRelVoidsElement FOR RelatingBuildingElement;
IsConnectionRealization : SET OF IfcRelConnectsWithRealizingElements FOR RealizingElements;
ProvidesBoundaries : SET OF IfcRelSpaceBoundary FOR RelatedBuildingElement;
ConnectedFrom : SET OF IfcRelConnectsElements FOR RelatedElement;
ContainedInStructure : SET [0:1] OF IfcRelContainedInSpatialStructure FOR RelatedElements;
ENTITY IfcFeatureElement
ENTITY IfcFeatureElementSubtraction
VoidsElements : IfcRelVoidsElement FOR RelatedOpeningElement;

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