Understanding Predecessors

Maximize schedule efficiency with task dependencies, known in ConstructionOnline™ as predecessors.

Predecessors are schedule tasks that must start or finish before another schedule task can start or finish. When a schedule task is set as a predecessor for another task, a predecessor relationship is created between the two tasks. A predecessor relationship acts as a link between the tasks, making one task dependent upon the other. Any changes to a predecessor task will affect other linked tasks—also referred to as successor tasks. 

There are four predecessor relationships available in ConstructionOnline's OnPlan™ Scheduling. 

Finish - Start 

The Finish-Start predecessor relationship means that a successor task cannot start until the predecessor task is complete. For example, let's say there are two Schedule Tasks: Task A and Task B. If Task A needs to be completely finished before Task B can begin, the Finish - Start predecessor relationship can be used to link the two tasks together. Now, even if delays occur or the schedule is altered, Task B (the successor task) will always start after Task A (the predecessor task) has finished.

This predecessor relationship is represented in ConstructionOnline by the format #fs, where # is the task number of the predecessor task. In the example above, Task B would be assigned a predecessor of 1fs (assuming Task A is task number 1). This is the default predecessor type used in ConstructionOnline; when schedule tasks are added sequentially to a schedule, ConstructionOnline automatically applies the Finish - Start predecessor to each task. This default setting can be turned off at any time in Schedule Task Options. 

Finish - Finish

The Finish-Finish predecessor relationship means that a successor task cannot finish until the predecessor task is complete. Both the predecessor task and successor task may run in parallel, but the successor task is not considered complete until the predecessor task has completely finished. For example, let's say there are two Schedule Tasks: Task A and Task B. After linking the two tasks together with the Finish-Finish predecessor relationship, Task B will not be able to completely finish until Task A has finished. 

This predecessor relationship is represented in ConstructionOnline by the format #ff, where # is the task number of the predecessor task. In the example above, Task B would be assigned a predecessor of 1ff (assuming Task A is task number 1). 

Start - Finish

The Start-Finish predecessor relationship means that a predecessor task cannot finish until the successor task has started. This predecessor relationship is not commonly used in scheduling, but may be occasionally used in situations where a handoff occurs between two tasks. For example, let's say there are two Schedule Tasks: Task A and Task B. After linking the two tasks together with the Start-Finish predecessor relationship, Task A will not be able to finish until Task B has started. 

This predecessor relationship is represented in ConstructionOnline by the format #sf, where # is the task number of the predecessor task. In the example above, Task B would be assigned a predecessor of 1sf (assuming Task A is task number 1). 

Start - Start

The Start-Start predecessor relationship means that a successor task cannot start until the predecessor task has started. For example, let's say there are two Schedule Tasks: Task A and Task B. After linking the two tasks together with the Start-Start predecessor relationship, Task B will not be able to start until Task A has started. 

This predecessor relationship is represented in ConstructionOnline by the format #ss, where # is the task number of the predecessor task. In the example above, Task B would be assigned a predecessor of 1ss (assuming Task A is task number 1).

Predecessor Lag Time

Predecessors can also have delay—commonly referred to as lag time. To add lag time to a predecessor, append a plus sign and the number of delay days to the existing predecessor format. For example: to add a 3 day delay to a task, the format 1fs+3 would be used. This means that the task will begin 3 days after the predecessor task (task number 1) is completed. Lag time may also be negative, resulting in an overlap instead of a delay. Negative lag time is also known as lead time. 

To learn how to set predecessors in a schedule, view Set Predecessors in a Schedule. 

HAVE MORE QUESTIONS?

• Frequently asked questions (FAQ) regarding OnPlan Scheduling can be found in the FAQ: Scheduling article. 
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