5.3.3.5 IfcRelSequence

5.3.3.5.1 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.

5.3.3.5.2 Entity inheritance

5.3.3.5.3 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, NOTE Only the last modification is stored - either as addition, deletion or modification. IFC4-CHANGE The attribute has been changed to be OPTIONAL.
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.
Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
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. IFC4-CHANGE Attribute added

Table 5.3.3.5.B

5.3.3.5.4 Formal propositions

Name	Description
AvoidInconsistentSequence	The RelatingProcess shall not point to the same instance as the RelatedProcess.
`RelatingProcess :<>: RelatedProcess`
CorrectSequenceType	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 5.3.3.5.C

5.3.3.5.5 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.
Click to show 2 hidden inherited concepts Click to hide 2 inherited concepts

Table 5.3.3.5.D

5.3.3.5.6 Examples

Figure 5.3.3.5.A

Construction Scheduling Task

5.3.3.5.7 Formal representation

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