5.3.3.6 IfcTask

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An IfcTask is an identifiable unit of work to be carried out in a construction project.

A task is typically used to describe an activity for the construction or installation of products, but is not limited to these types. For example it might be used to describe design processes, move operations and other design, construction and operation related activities as well.

Quantities of resources consumed by the task are dealt with by defining the IfcElementQuantity for the resource and not at the instance of IfcTask.

HISTORY  New entity in IFC1.0. Renamed from IfcWorkTask in IFC2x.
IFC4 CHANGE  Attributes TaskTime and PredefinedType added. IfcMove and IfcOrderRequest has been removed in IFC4 and are now represented by IfcTask. IfcRelAssignsTasks relationship has been removed as well.

Attribute use definition

Each occurrence of IfcTask is given a name that is indicative of its content (IfcRoot.Name). A textual description of the task may be provided and this may be further elaborated by a narrative long description (IfcProcess.LongDescription). A work method may be declared for the method of work used in carrying out a task. A task is identified as being either a milestone task or not. A milestone task is defined by the marker IsMilestone. and has no duration. A status and priority for each task may also be set.

Time and duration use definition

Compared to previous IFC releases, basic task time information (scheduled start time, scheduled finish time, duration) is now directly attached to IfcTask through the TaskTime attribute. Regular tasks are defined through IfcTaskTime. Recurring tasks are defined through IfcTaskTimeRecurring. In case a regular task is derived from a recurring task both tasks should be linked together through a IfcRelNests relationship, where IfcRelNests.IsNestedBy points to the recurring task and IfcRelNests.Nests points to all regular tasks that have been derived from the recurring task.

Representation of other activities

The use definitions for IfcTask have been generalised to represent other activities as well, including activities that had been defined by own entities in previous IFC releases. This includes

IfcTask represents an order that might be carried out by a Helpdesk acting the role of interface for the organization between the facility user and the functional requirement of fulfilling their needs. The actual task represented by the IfcTask entity is turning a request into an order and initiating the action that will enable the order to be completed. The IfcProjectOrder or one of its subtypes including maintenance work order, is related to the IfcTask using IfcRelAssignsToControl.

IfcTask can also be used to describe an activity that moves people, groups within an organization or complete organizations together with their associated furniture and equipment from one place to another. It thus replaces the previous IFC entity IfcMove. The functionality is represented in IfcTask as follows:


Common Use Definitions

The following concepts are inherited at supertypes:

 Instance diagram

Object Typing

The Object Typing concept applies to this entity as shown in Table 14.
Type
IfcTaskType

Table 14 — IfcTask Object Typing

The IfcTask defines the anticipated or actual occurrence of any task; common information about task types is handled by IfcTaskType.

EXAMPLE  It includes fixed duration, fixed unit or fixed work. An IfcTask can be aggregated to a task type in order to specify a task sequence or any time related information, e.g. the duration of a task. Please see the documentation of IfcTaskType for further information.


Property Sets for Objects

The Property Sets for Objects concept applies to this entity as shown in Table 15.
PredefinedTypeName
 Pset_Risk

Table 15 — IfcTask Property Sets for Objects



Object Nesting

The Object Nesting concept applies to this entity.

IfcTask may be contained within an IfcTask using the IfcRelNests relationship. An IfcTask may in turn nest other IfcTask, IfcProcedure or IfcEvent entities. Such nesting indicates decomposed level of detail. From IFC4 onwards it is required to have a summary task (root of all tasks), which is used to define a link to the work plan or work schedule. All subtasks of the summary tasks are then implicitly linked to this work plan or work schedule. Please note that the summary task is used for data organization and not meant to store typical task information as defined by the user. It is therefore recommended that the summary task is hidden from the user to avoid confusion. Please also note that IfcRelNests is used to show the dependency between regular tasks and recurring task definitions (please see the section about time and duration use definitions).

As shown in Figure 104, the installation of a number of items of equipment within a particular space may be the subject of a single task which is identified as 'fix equipment in space 123'. IfcTask represents the occurrence of a work performance of a type of process in a construction plan.

task example

Figure 104 — Task visualization

A task may nest other tasks as sub-items; the nesting relationship is modeled by IfcRelNests as shown in Figure 105. For example, the construction of a stud wall may be designated as a nesting task named 'install wall #1' including other tasks such as 'install dry wall', 'install studs', 'wall taping', and 'erect wall' as sub-processes. A value that indicates the relative tree view position of the task (in comparison to the tree view position of other tasks and the task hierarchy defined by IfcRelNests).

The task order information that is used for viewing purposes is derived from the order defined by the IfcRelNests relationship and thus is independent of the logical task order defined through IfcRelSequence. The hierarchy and order defined through IfcRelNests enables to order the tasks in a tree view or list view structure.

task instantiation diagram

Figure 105 — Task nesting relationships



Sequential Connectivity

The Sequential Connectivity concept applies to this entity.

The relationship IfcRelSequence is used to indicate control flow. An IfcTask as a successor to an IfcTask indicates logical sequence how these tasks should be performed. IfcTask's can be triggered or can trigger IfcEvent's, which is also defined through the relationship IfcRelSequence.



Control Assignment

The Control Assignment concept applies to this entity.

Occurrences of IfcTask may be assigned to an IfcWorkControl (either a work plan or a work schedule) through IfcRelAssignsToControl. Please note that the IfcRelAssignsTasks relationship class has been removed in IFC4 and is no longer available.



Process Assignment

The Process Assignment concept applies to this entity.

It is suggested to use the 'summary task' (root element of the task hierarchy that is required for task management purposes) to assign all subtask to a work plan or work schedule. Resources used by tasks are assigned by IfcRelAssignsToProcess.



Product Assignment

The Product Assignment concept applies to this entity.



Object Classification

The Object Classification concept applies to this entity.

An IfcTask may be assigned a Work Breakdown Structure (WBS) code. A WBS code is dealt with as a classification of task and is associated to a task occurrence using the IfcRelAssociatesClassification relationship class. As well as being to designate the code, the classification structure also enables the source of the work breakdown structure classification to be identified.



Object Constraint

The Object Constraint concept applies to this entity as shown in Table 16.
DataValueAttribute1Attribute2Description
   Indicate fixed duration of task with ConstraintGrade=HARD and Benchmark=EQUALTO such that changes to an assigned IfcConstructionResource.ResourceTime.ScheduleWork should impact IfcConstructionResource.ResourceTime.ScheduleUsage, and vice-versa.

Table 16 — IfcTask Object Constraint

Constraints may be applied to a task to indicate fixed task duration, fixed start or fixed finish (see Figure 147). The relationship IfcRelAssociatesConstraint is used where RelatingConstraint points to an IfcMetric and RelatedObjects includes the IfcTask. IfcRelAssociatesConstraint.Name identifies the attribute to be constrained using a period (".") to dereference; for example, "TaskTime.ScheduleStart" refers to the ScheduleStart attribute on the IfcTaskTime entity referenced on the TaskTime attribute. The following attributes may be constrained (see Table 11 with Constrained Attribute):

A "manual scheduled task" is indicated with ConstraintGrade=HARD and Benchmark=EQUALTO for both TaskTime.ScheduleStart and TaskTime.ScheduleFinish.

task time constraint example

Figure 106 — Task constraints




XSD Specification:

 <xs:element name="IfcTask" type="ifc:IfcTask" substitutionGroup="ifc:IfcProcess" nillable="true"/>
 <xs:complexType name="IfcTask">
  <xs:complexContent>
   <xs:extension base="ifc:IfcProcess">
    <xs:sequence>
     <xs:element name="TaskTime" type="ifc:IfcTaskTime" nillable="true" minOccurs="0"/>
    </xs:sequence>
    <xs:attribute name="Status" type="ifc:IfcLabel" use="optional"/>
    <xs:attribute name="WorkMethod" type="ifc:IfcLabel" use="optional"/>
    <xs:attribute name="IsMilestone" type="xs:boolean" use="optional"/>
    <xs:attribute name="Priority" type="xs:long" use="optional"/>
    <xs:attribute name="PredefinedType" type="ifc:IfcTaskTypeEnum" use="optional"/>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>

EXPRESS Specification:

ENTITY IfcTask
SUBTYPE OF IfcProcess;
Status : OPTIONAL IfcLabel;
WorkMethod : OPTIONAL IfcLabel;
IsMilestone : BOOLEAN;
Priority : OPTIONAL INTEGER;
TaskTime : OPTIONAL IfcTaskTime;
PredefinedType : OPTIONAL IfcTaskTypeEnum;
WHERE
HasName : EXISTS(SELF\IfcRoot.Name);
CorrectPredefinedType : NOT(EXISTS(PredefinedType)) OR (PredefinedType <> IfcTaskTypeEnum.USERDEFINED) OR ((PredefinedType = IfcTaskTypeEnum.USERDEFINED) AND EXISTS(SELF\IfcObject.ObjectType));
END_ENTITY;

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

Status : Current status of the task.
NOTE  Particular values for status are not specified, these should be determined and agreed by local usage. Examples of possible status values include 'Not Yet Started', 'Started', 'Completed'.
WorkMethod : The method of work used in carrying out a task.
NOTE  This attribute should not be used if the work method is specified for the IfcTaskType
IsMilestone : Identifies whether a task is a milestone task (=TRUE) or not (= FALSE).
NOTE  In small project planning applications, a milestone task may be understood to be a task having no duration. As such, it represents a singular point in time.
Priority : A value that indicates the relative priority of the task (in comparison to the priorities of other tasks).
TaskTime : Time related information for the task.
IFC4 CHANGE Attribute added
PredefinedType : Identifies the predefined types of a task from which the type required may be set.
IFC4 CHANGE Attribute added

Formal Propositions:

HasName : The Name attribute should be inserted to describe the task name.
CorrectPredefinedType : The attribute ObjectType must be asserted when the value of PredefinedType is set to USERDEFINED.

Inheritance Graph:

ENTITY IfcTask
ENTITY IfcRoot
GlobalId : IfcGloballyUniqueId;
OwnerHistory : OPTIONAL IfcOwnerHistory;
Name : OPTIONAL IfcLabel;
Description : OPTIONAL IfcText;
ENTITY IfcObjectDefinition
INVERSE
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;
INVERSE
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 IfcProcess
Identification : OPTIONAL IfcIdentifier;
LongDescription : OPTIONAL IfcText;
INVERSE
IsPredecessorTo : SET OF IfcRelSequence FOR RelatingProcess;
IsSuccessorFrom : SET OF IfcRelSequence FOR RelatedProcess;
OperatesOn : SET OF IfcRelAssignsToProcess FOR RelatingProcess;
ENTITY IfcTask
Status : OPTIONAL IfcLabel;
WorkMethod : OPTIONAL IfcLabel;
IsMilestone : BOOLEAN;
Priority : OPTIONAL INTEGER;
TaskTime : OPTIONAL IfcTaskTime;
PredefinedType : OPTIONAL IfcTaskTypeEnum;
END_ENTITY;

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