|Teil zu Ganzes Beziehung - Relation (allgemein)|
The decomposition relationship, IfcRelDecomposes, defines the general concept of elements being composed or decomposed. The decomposition relationship denotes a whole/part hierarchy with the ability to navigate from the whole (the composition) to the parts and vice versa.
Decompositions may be constrained by requiring both, the whole and its parts, to be of the same type - thus establishing a nesting relationship. Or they may require some form of physical containment, thus establishing special types of aggregation relationships.
NOTE There are two special names for decomposition, which are linguistically distinguished, nesting and aggregation. The subtypes of IfcRelDecomposes will introduce either the nesting or aggregation convention (see IfcRelNests and IfcRelAggregates).
EXAMPLE A cost element is a nest of other cost elements. Or a structural frame is an aggregation of beams and columns. Both are applications of decomposition relationship.
Decompositions imply a dependency, i.e. the definition of the whole depends on the definition of the parts and the parts depend on the existence of the whole. The decomposition relationship can be applied in a recursive manner, i.e. a decomposed element can be part in another decomposition. Cyclic references have to be prevented at application level.
HISTORY New entity in IFC1.5, it is a generalisation of the IFC2.0 entity IfcRelNests.
IFC4 CHANGE The differentiation between the aggregation and nesting is determined to be a non-ordered or an ordered collection of parts. The attributes RelatingObject and RelatedObjects have been demoted to the subtypes.
|1||GlobalId||IfcGloballyUniqueId||[1:1]||Assignment of a globally unique identifier within the entire software world.||X|
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.
|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|
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