Dependencies are relationship links between tasks that are used when scheduling and rescheduling a project over the duration of the project. They are of the form of:
- Finish-to-Start Task Dependency (FS) - a finish-to-start dependency occurs when the initial task must be completed for the next task to begin. As such, if task A is completed behind schedule then task B will begin behind schedule as well, creating a domino effect.
- Start-to-Start Task Dependency (SS) - a start-to-start dependency occurs when a secondary task cannot begin until the initial task begins. Now, it’s important to note that the two tasks do not have to begin at the same time (and often do not). Task B can begin well after task A, so long as task A has started. In many cases, the initial task will even finish before the next task begins. But, because task A does not have to be completed before task B can begin, this is not a finish-to-start dependency.
- Finish-to-Finish Task Dependency (FF) - a finish-to-finish dependency refers to a situation in which the initial task must be completed in order for the following task to be completed. Task A and task B are directly related, and these two tasks can even take place at the same time, but task B is totally contingent on task A. That said, task B does not have to be finished at the same time as task A.
- Start-to-Finish Task Dependency (SF) - start-to-finish dependencies are uncommon. In a start-to-finish dependency, the initial task cannot be finished until the secondary task has begun. That being said, task B does not have to finish at the same moment task A begins.
In addition to the dependencies there are two other features that can be attributed to them:
- Lead: If in the case of two tasks A and B where A must finish before A starts ie Finish to Start (FS) but B is planned or as a result of scheduling can start before A is finished then this can be represented by a negative lead. IE FS-2d means that B can start 2 days prior to the finish of Task A and will always do so in a scheduled project.
- Lag: If in the case of two tasks A and B where A must finish before A starts ie Finish to Start (FS) but A is planned or as a result of scheduling can start before B is finished then this can be represented by a positive lead. IE FS+2d means that B can start 2 after the finish of Task A and will always do so in a scheduled project.
The default type of a dependency is "Finish-to-Start" (FS). This type of dependency restricts the dependent task to not start earlier than the end date of the preceding task.
With this dependency type, the succeeding task is delayed to not start earlier than the start of the preceding task.
The succeeding task cannot finish before the completion of the preceding task.
The finish of the succeeding task is constrained by the start of the preceding task. The successor cannot finish before the predecessor starts.
A dependency can have a lag (or lead) value which can delay the succeeding event by the number of lag units specified.
Lead (or "negative lag") will accelerate the succeeding event by the number of time units specified.
Please note, the lag value specifies the amount of working time. The calendar controlling which time to use is defined by the calendar field. By default, the successor calendar is used.
Please note, the lag value specifies the amount of working time. The calendar controlling which time to use is defined by the calendar field. By default, the successor calendar is used.
Adding dependencies to your tasks
To add a dependencies there are several methods:
- Directly enter select the dependencies Predecessors or Successors column in the task list (if not visible right click in the header, then column to add). Select the task and the dependency entry and type in the dependency using the following nomenclature plus and lead or lag in days.
- Finish-to-Start Task Dependency (FS)
- Start-to-Start Task Dependency (SS)
- Finish-to-Finish Task Dependency (FF)
- Start-to-Finish Task Dependency (SF)
- Right click on the task in the Gantt chart or the task list and open the Task Information window.
- Click on either the {PREDECESSORS} or the {SUCCESSORS} tabs
- Click [+] to add a new entry line
- Select the task.
- Select the dependency type.
- Enter the lead or lag if required.
- Click [Save]
- Directly entry select the Dependencies column in the task list (if not visible right click in the header, the column to add). Click the downward triangle
- Select multiple links by clicking either end of the small rectangular boxes. Links will be green and the dots show the link dependency.
- Selecting one of the small dots on either end of the Gantt chart bar for task A
- Then draw by dragging the link from one task bar to one end of the task bar for task B. Lead or Lag can be added via the Task Information window or via the Predecessor/Successor columns.
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