There are four main relationships among tasks in Gantt charts: start-to-finish (SF), finish-to-start (FS), finish-to-finish (FF), and start-to-start (SS). These are all relationships that two tasks may have with each other. SF refers to when the start of one task connects to the finish of another task. FS refers to when the completion of one task connects to the start of another. FF refers to two tasks that must be completed at the same time and SS refers to two tasks that must begin simultaneously.
However, the distinction between FS and SF is unclear to me. The start and finish of tasks are connected in both instances, so I am unsure of the distinction between them. In the lecture, FS was explained as not being able to complete Task B until Task A is completed, and SF was explained as the start of Task A being connected to the finish of Task B. The only difference in this explanation to me is the switching of the variables A and B, so I don't fully understand the distinction. I would appreciate any explanations and examples that clearly highlight the differences between FS and SF tasks.
In an FS dependency, the start of one task depends on the completion of another task. As you said, task B cannot start until task A is finished. For example, task A is "cutting wood" and task B is "shaping wood". So task B cannot begin until the wood is cut and available for shaping. Whereas, in an SF dependency, the completion of one task depends on the start of another task. As you mentioned, task A will start when task B finishes. For example, at a small event like a wedding, task A is to "sit everyone to their seats" and task B is to "welcome the arriving guests." So we cannot start seating guests before they arrive at the event. I hope these examples help you to better clarify the differences between FS and SF dependencies.
The key distinction between FS and SF is the direction of dependency. FS can be described as having a "forward-looking" dependency where Task B's start is dependent on Task A's finish. SF can be described as an almost "backward-looking" dependency where Task B's finish is dependent on Task A's start. Moreover, FS relationships are sequential and are about the progress of a project where one must finish one task to start another. On the other hand, SF relationships are more related to closure and transitioning of tasks where starting something new allows the closure of something old. I believe your confusion arises from the fact that both types of relationship involve starting and finishing; however, as long as you remember that in FS the completion results in the beginning of another task, and in SF the beginning of one task results in the completion of another, you should be able to distinguish between them.
I’ll be providing a start-to-finish relationship example that occurred a few semesters ago on campus. The implementation of the new parking tapping card access system must be completed before the old swiping card access system is removed represents a SF relationship. The roll-out of the new access system is required to be able to remove the original access system. The next example relates to the writing process. An example of a finish-to-start relationship is: a report must be drafted before it can be edited. The finish date of the report draft determines the start date of the editing process. When drafting is completed, the editing process can start.
