IfcElementAssembly

Semantic definitions at the entity

Entity definition

A container class that represents complex element assemblies aggregated from several elements, such as discrete elements, building elements, or other elements.

EXAMPLE Steel construction assemblies, such as trusses and different kinds of frames, can be represented by the IfcElementAssembly entity. Other examples include slab fields aggregated from a number of precast concrete slabs or reinforcement units made from several reinforcement bars.

HISTORY New Entity for Release IFC2x Edition 2.

Containment Use Definition

The IfcElementAssembly should have (and in most implementation scenarios it is mandatory) a relationship for its hierarchical containment in the spatial structure of the project.

The IfcElementAssembly is placed within the project spatial hierarchy using the objectified relationship IfcRelContainedInSpatialStructure, referring to it by its inverse attribute SELF\IfcElement.ContainedInStructure. Subtypes of IfcSpatialStructureElement are valid spatial containers, with IfcBuildingStorey being the default container.

The IfcElementAssembly shall represent an aggregate, i.e. it should have other elements, being subtypes of IfcElement, as contained (sub)parts.

The IfcElementAssembly is an aggregate i.e. being composed by other elements and acting as an assembly using the objectified relationship IfcRelAggregates, referring to it by its inverse attribute SELF\IfcObjectDefinition.IsDecomposedBy. Components of an assembly are described by instances of subtypes of IfcElement.
In this case, the contained subtypes of IfcElement shall not be additionally contained in the project spatial hierarchy, i.e. the inverse attribute SELF\IfcElement.ContainedInStructure of those IfcElement's shall be NIL.

FIGURE spatial containment and element aggregation relationships for IfcElementAssembly

Geometry Use Definitions

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

Local Placement

The local placement for IfcElementAssembly 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 PlacementRelTo relationship of IfcLocalPlacement shall point (if given) to the local placement of the same IfcSpatialStructureElement that is used in the ContainedInStructure inverse attribute or to a referenced spatial structure element at a higher level.
If the relative placement is not used, the absolute placement is defined within the world coordinate system.

Geometric Representations

The geometry of an IfcElementAssembly is generally formed from its components, in which case it does not need to have an explicit geometric representation. In some cases it may be useful to also expose a simple explicit representation as a bounding box representation of the complex composed shape independently.

Informal proposition

The IfcElementAssembly shall have an aggregation relationship to the contained parts, i.e. the (INV) IsDecomposedBy relationship shall be utilized.

Attribute definitions

#	Attribute	Type	Cardinality	Description	A
9	AssemblyPlace	-		This attribute is out of scope for this model view definition and shall not be set.
10	PredefinedType	IfcElementAssemblyTypeEnum	[1:1]	Predefined generic types for a element assembly that are specified in an enumeration.	X

Formal Propositions

Rule	Description
WR1	The attribute ObjectType shall be given, if the predefined type is set to USERDEFINED.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	A
IfcRoot
1	GlobalId	IfcGloballyUniqueId	[1:1]	Assignment of a globally unique identifier within the entire software world.	X
2	OwnerHistory	IfcOwnerHistory	[1:1]	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.	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
	IsDecomposedBy	IfcRelDecomposes @RelatingObject	S[0:?]	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.	X
	Decomposes	IfcRelDecomposes @RelatedObjects	S[0:1]	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).	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
IfcObject
5	ObjectType	IfcLabel	[0:1]	The type denotes a particular type that indicates the object further. The use has to be established at the level of instantiable subtypes. In particular it holds the user defined type, if the enumeration of the attribute PredefinedType is set to USERDEFINED.	X
	IsDefinedBy	IfcRelDefines @RelatedObjects	S[0:?]	Set of relationships to type or property (statically or dynamically defined) information that further define the object. In case of type information, the associated IfcTypeObject contains the specific information (or type, or style), that is common to all instances of IfcObject referring to the same type.	X
IfcProduct
6	ObjectPlacement	IfcObjectPlacement	[0:1]	Placement of the product in space, the placement can either be absolute (relative to the world coordinate system), relative (relative to the object placement of another product), or constraint (e.g. relative to grid axes). It is determined by the various subtypes of IfcObjectPlacement, which includes the axis placement information to determine the transformation for the object coordinate system.	X
7	Representation	IfcProductRepresentation	[0:1]	Reference to the representations of the product, being either a representation (IfcProductRepresentation) or as a special case a shape representations (IfcProductDefinitionShape). The product definition shape provides for multiple geometric representations of the shape property of the object within the same object coordinate system, defined by the object placement.	X
IfcElement
8	Tag	-		This attribute is out of scope for this model view definition and shall not be set.
	ConnectedTo	IfcRelConnectsElements @RelatingElement	S[0:?]	Reference to the element connection relationship. The relationship then refers to the other element to which this element is connected to.
	HasOpenings	IfcRelVoidsElement @RelatingBuildingElement	S[0:?]	Reference to the Voids Relationship that creates an opening in an element. An element can incorporate zero-to-many openings.	X
	IsConnectionRealization	IfcRelConnectsWithRealizingElements @RealizingElements	S[0:?]	Reference to the connection relationship with realizing element. The relationship then refers to the realizing element which provides the physical manifestation of the connection relationship.	X
	ConnectedFrom	IfcRelConnectsElements @RelatedElement	S[0:?]	Reference to the element connection relationship. The relationship then refers to the other element that is connected to this element.	X
	ContainedInStructure	IfcRelContainedInSpatialStructure @RelatedElements	S[0:1]	Containment relationship to the spatial structure element, to which the element is primarily associated.	X
IfcElementAssembly
9	AssemblyPlace	-		This attribute is out of scope for this model view definition and shall not be set.
10	PredefinedType	IfcElementAssemblyTypeEnum	[1:1]	Predefined generic types for a element assembly that are specified in an enumeration.	X

Definitions applying to AISC Model View

Instance diagram

An assembly represents a fabricated steel element consists of a main piece with attached sub pieces. An assembly belongs to a spatial structure through Contained in Spatial Structure Relationship (IfcRelContainedInSpatialStructure). Assembly's local coordinate becomes the reference placement for pieces, of which local coordinate becomes the reference placement for attached accessories respectively.

An assembly's geometric representation should be derived from its main piece and sub pieces and should not have its own geometric representation.

Assembly marks of adjacent assemblies are not explictily defined, it can be listed from the other assemblies listed in the Contained in Spatial Structure Relationship, or should be calculated with the users' own adjacency specification from the location of the other assemblies in the relationship.

Assembly may have attributes listed below should use Defines By Property Set (IfcRelDefinesByPropertyies) in order to represent required information items listed below and are described in the corresponding sections of this document.

Assembly Identification

GUID
Assembly name
Assembly mark
Client mark
Prelim mark
Shipping mark
Bar code

Status Information

Status flags

Scheduling information

Sequence ID
Sequence level
On site by date

Drawing Information

Drawing numbers

Quantity Information

Count

Version

Version number

Finish/ Treatment

Surface treatment

Steel Detailing Information	IFC Entity\Attribute	Note
Spatial Location	IfcRelContainedInSpatialStructure	Assembly is belong to Spatial Structure
Components	IfcRelAggregates	Pieces belong to Assembly
Spatial structure	IfcRelContainedInSpatialStructure

Concept usage

Properties on Occurrences

The Properties on Occurrences concept applies to this entity as shown in Table 3.

Property
AISC_EM11_Pset_AssemblyIdentification
AISC_EM11_Pset_DrawingNumber
AISC_EM11_Pset_VersionInformation
AISC_EM11_Pset_SchedulingInformation
AISC_EM11_Pset_ToleranceForLayout
AISC_EM11_Pset_Material
AISC_EM11_Pset_StatusInformation

Table 3 — IfcElementAssembly Properties on Occurrences

Exchange
Import	O
Export	O

Spatial Containment

The Spatial Containment concept applies to this entity as shown in Table 4.

RelatingSpatialStructure
IfcBuildingStorey

Table 4 — IfcElementAssembly Spatial Containment

Exchange
Import	R
Export	R

Quantities on Occurrences

The Quantities on Occurrences concept applies to this entity as shown in Table 5.

Qset	Quantity	Description
AISC_EM11_Qto_Quantity	SameTypeCount	Number of assemblies with same assembly mark. Used on occuerrence, even though it should be used for type count for implementation convenience

Table 5 — IfcElementAssembly Quantities on Occurrences

Exchange
Import	O
Export	O

Grid Placement

The Grid Placement concept applies to this entity.

Exchange
Import	O
Export	O

Placement

The Placement concept applies to this entity.

Exchange
Import	O
Export	O

Material Solid

The Material Solid concept applies to this entity.

Exchange
Import	O
Export	O

Concept inheritance

#	Concept	Model View
IfcElementAssembly
	Properties on Occurrences	AISC Model View
	Spatial Containment	AISC Model View
	Quantities on Occurrences	AISC Model View
	Grid Placement	AISC Model View
	Placement	AISC Model View
	Material Solid	AISC Model View

Formal representations

XSD Specification

 <xs:element name="IfcElementAssembly" type="ifc:IfcElementAssembly" substitutionGroup="ifc:IfcElement" nillable="true"/>

 <xs:complexType name="IfcElementAssembly">

  <xs:complexContent>

   <xs:extension base="ifc:IfcElement">

    <xs:attribute name="PredefinedType" type="ifc:IfcElementAssemblyTypeEnum" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcElementAssembly

 SUBTYPE OF (IfcElement);

  AssemblyPlace : OPTIONAL IfcStrippedOptional;

  PredefinedType : IfcElementAssemblyTypeEnum;

 WHERE

  WR1 : (PredefinedType <> IfcElementAssemblyTypeEnum.USERDEFINED) OR ((PredefinedType = IfcElementAssemblyTypeEnum.USERDEFINED) AND EXISTS(SELF\IfcObject.ObjectType)) ;
END_ENTITY;

 EXPRESS-G diagram

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