Links between tasks

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Links between tasks affect the planned start and end dates of tasks. Links between tasks do not result in the creation or automatic completion of tasks, and no other system behavior is triggered when tasks are linked, apart from changing planned start and end dates.


If task B depends on task A, then task A is called the "predecessor," and task B is called the "successor." Links between tasks are designed to automatically change the planned dates of the successor when the dates of the predecessor are changed.


Managing links

You can add or modify links between tasks:


Types of links

Planfix supports four types of links between tasks


Finish-To-Start

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This is the most frequently used link. If you establish this link, the planned start date of task B must be after the planned completion date of task A. When you push back the completion date of task A past the start date of task B, task B's start date will automatically be pushed back to the earliest possible date.


If the completion date of task A is moved earlier again, the start date of task B will move earlier, too, although it will not be moved earlier than its initial start date. For example, let's say the initial completion date of task A was 1/20/15, task B was supposed to start on 1/21/15, and the two tasks had a Finish-To-Start link.

  • If the completion date of task A was moved to 1/22/15, the start date of task B would be set to 1/23/15.
  • If task A's completion date were moved to 1/23/15, task B would start on 1/26/15, since 1/24 and 1/25 are weekend days (assuming the assignee doesn't have weekends set as working days)
  • If the completion date of task A was moved back to 1/22/15, the start date of task B would be set to 1/23/15 again.
  • If the completion date of task A was then moved to 1/16/15, the start date of task B would be set back to 1/21/15 (its original start date)


Start-To-Start

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The planned start date of task B must be the same or later than the planned start date of task A. Task B cannot start until task A has started. This type of link doesn't require both tasks to start at the same time. Task B can start at any time after task A has started.


Example

In order to save time in a construction project, it was decided to level the concrete on one side of a foundation while concrete was still being poured on the other side. But the task Leveling Concrete (Task B) can't start before Pouring Concrete (Task A) has started.


Start-To-Finish

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The planned completion date of task B must be the same or later than the planned start date of task A. Task B cannot be finished until task A has started. Task B can finish any time after task A has started. This type of link is rarely used.


Example

Trusses for a building are built outside the construction site. The task Assemble Roof (Task B) can't be completed until the task Deliver Trusses (Task A) has started.


Finish-To-Finish

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The planned completion date of task B must be the same or later than the planned completion date of task A.


Task B cannot be finished until task A has been finished. This type of link doesn't require both tasks to be completed at the same time. Task B can finish any time after task A has been finished. Example. A group is installing electrical wiring in a building and testing the electrical equipment. They can't complete the task of Testing the Electrical Equipment (Task B) until they have completed the task of Installing Electrical Wiring (Task A).


Delays

The dependency between tasks A and B can be more complicated than just "task B starts after task A has been finished." It's possible for task B to need to start two days before task A has been completed, or maybe three days after. To make this work, a delay is used, which can be set when configuring the task dependency


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Task and subtasks

Hierarchical dependencies between tasks also create dependencies between their dates: the completion dates of all subtasks must be earlier than the completion date of the parent task. When setting subtask dates later than the dates of their parent task, the parent task date will automatically be pushed back (if the employee modifying the date has permissions to edit the parent task).


Therefore, to avoid cyclic links, only the following links are allowed between tasks and subtasks:

  • Start-To-Start from parent task to subtask
  • End-To-End from subtask to parent task


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