IFC (IFC4X3_ADD2) under development IfcRelSequence Semantic definition

IfcRelSequence is a sequential relationship between processes where one process must occur before the other in time and where the timing of the relationship may be described as a type of sequence. The relating process (IfcRelSequence.RelatingProcess) is considered to be the predecessor in the relationship (has precedence) whilst the related process (IfcRelSequence.RelatedProcess) is the successor.

IfcRelSequence is defined as one-to-one relationship; therefore it assigns one predecessor to one successor.

Use definitions

IfcRelSequence is used to describe the logical sequence relationship that exists between two processes. This logical relationship identifies that there is a predecessor or relating process and a successor or related process. In IFC, there may be one predecessor and one successor in the relationship. Many occurrences of IfcRelSequence may exist to describe the sequence relationships of a predecessor task with many successor tasks or of many predecessor tasks with one successor task, thus enabling a m:n sequence relationship between tasks. Please note that sequence relationships can be used to define dependencies between process occurrences but also between process types (for further information see IfcRelDefinesByObject and IfcTaskType). In case of defining dependencies between process occurrences sequence relationships should stay within the limits of a directed, non-cyclic graph.

A sequence type may be set for a sequence. For tasks assigned to a work schedule, it is expected that the sequence type will be asserted. For a process map, where the sequence relationship between processes is simply a logical flow, it need not be asserted.

A time lag may be assigned to a sequence, and the sequence type defines the way in which the time lag applies to the sequence either as a ratio or percentage of time duration (e.g. start successor task when predecessor is 50% complete) or as a time measure (e.g. start successor task 1 week after commencement of the predecessor task). Care should be used when assigning a time lag to a sequence depending on the setting of the sequence type since there is no checking that the time lag value is in keeping with the sequence type set. Entity inheritance Attributes

# Attribute Type Description
IfcRoot (4)
1 GlobalId IfcGloballyUniqueId

Assignment of a globally unique identifier within the entire software world.

2 OwnerHistory OPTIONAL IfcOwnerHistory

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,

3 Name OPTIONAL IfcLabel

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.

4 Description OPTIONAL IfcText

Optional description, provided for exchanging informative comments.

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IfcRelSequence (5)
5 RelatingProcess IfcProcess

Reference to the process, that is the predecessor.

6 RelatedProcess IfcProcess

Reference to the process, that is the successor.

7 TimeLag OPTIONAL IfcLagTime

Time duration of the sequence, it is the time lag between the predecessor and the successor as specified by the SequenceType.

8 SequenceType OPTIONAL IfcSequenceEnum

The way in which the time lag applies to the sequence.

9 UserDefinedSequenceType OPTIONAL IfcLabel

Allows for specification of user defined type of the sequence beyond the enumeration values (START_START, START_FINISH FINISH_START, FINISH_FINISH) provided by SequenceType attribute of type IfcSequenceEnum. When a value is provided for attribute UserDefinedSequenceType in parallel the attribute SequenceType shall have enumeration value USERDEFINED.

Table Formal propositions

Name Description

The RelatingProcess shall not point to the same instance as the RelatedProcess.

RelatingProcess :<>: RelatedProcess

The attribute UserDefinedSequenceType must be asserted when the value of SequenceType is set to USERDEFINED.

(SequenceType <> IfcSequenceEnum.USERDEFINED) OR ((SequenceType = IfcSequenceEnum.USERDEFINED) AND EXISTS(UserDefinedSequenceType))
Table Concept usage

Concept Usage Description
IfcRoot (2)
Revision Control General

Ownership, history, and merge state is captured using IfcOwnerHistory.

Software Identity General

IfcRoot assigns the globally unique ID. In addition it may provide for a name and a description about the concept.

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Table Examples Formal representation

ENTITY IfcRelSequence
 SUBTYPE OF (IfcRelConnects);
	RelatingProcess : IfcProcess;
	RelatedProcess : IfcProcess;
	TimeLag : OPTIONAL IfcLagTime;
	SequenceType : OPTIONAL IfcSequenceEnum;
	UserDefinedSequenceType : OPTIONAL IfcLabel;
	AvoidInconsistentSequence : RelatingProcess :<>: RelatedProcess;
	CorrectSequenceType : (SequenceType <> IfcSequenceEnum.USERDEFINED) OR ((SequenceType = IfcSequenceEnum.USERDEFINED) AND EXISTS(UserDefinedSequenceType));
END_ENTITY; References

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Is this page difficult to understand? Let us know! Changelog IFC4

  • attribute, UserDefinedSequenceType
  • where rule, AvoidInconsistentSequence
  • where rule, CorrectSequenceType
  • where rule, WR1
  • attribute SequenceType optional, Is now optional
  • attribute TimeLag optional, Is now optional
  • attribute TimeLag type, Changed from "IfcTimeMeasure" to "IfcLagTime"