Task Relationships
Task Relationships are the links between the tasks in the Dependency Chart. There are four main relationship types:
- Finish to Start
- Start to Start
- Finish to Finish
- Start to Finish
We will look at each in turn. Each Relationship Type can also be affected by Lead Time and Lag Time.
Finish to Start
The Finish to Start relationship means that the first task must finish before the second task can start. In the Dependency chart it is shown as follows. The ‘X’ denotes the Lead Time (a negative number) or Lag Time (a positive number).
Finish to Start
On a Gantt Chart, the dependencies will look like the following diagram. Firstly with no Lead or Lag, secondly with Lag Time, and finally with Lead Time.
Finish to Start Gantt
This is the most common type of relationship type.
Start to Start
The Start to Start relationship means that the first task and the second task should start at the same time. In the Dependency chart it is shown as follows. The ‘X’ denotes the Lead Time (a negative number) or Lag Time (a positive number).
Start to Start
On a Gantt Chart, the dependencies will look like the following diagram. Firstly with no Lead or Lag, secondly with Lag Time, and finally with Lead Time.
Start to Start Gantt
The same could be achieved by using a Finish to Start relationship type, and adding Lead Time to equal the duration of the first task.
Finish to Finish
The Finish to Finish relationship means that the first task must finish at the same time as the second task. In the Dependency chart it is shown as follows. The ‘X’ denotes the Lead Time (a negative number) or Lag Time (a positive number).
Finish to Finish
On a Gantt Chart, the dependencies will look like the following diagram. Firstly with no Lead or Lag, secondly with Lag Time, and finally with Lead Time.
Finish to Finish Gantt
This relationship type has arrows pointing from right to left, which can be very confusing.
Start to Finish
The Finish to Start relationship means that the first task cannot start second task has finished. In the Dependency chart it is shown as follows. The ‘X’ denotes the Lead Time (a negative number) or Lag Time (a positive number).
Start to Finish
On a Gantt Chart, the dependencies will look like the following diagram. Firstly with no Lead or Lag, secondly with Lag Time, and finally with Lead Time.
Start to Finish Gantt
Again, this relationship type has arrows pointing from right to left. The same affect could be achieved by doing the tasks in the other order.
Summary
That covers the four different relationship types. Lead Time and Lag Time complicate the relationships.
Keep it simple. Use Finish to Start Relationships by default, and only use the other types where absolutely necessary.
