How To Manage Task Dependencies
What are those thin lines between tasks on your project schedule? They are dependencies — links between tasks showing the relationships between the activities. Think of them as helping you work out which order you need to complete your tasks in, a bit like turning your task list into a flow diagram.
Dependencies are normally marked on your project schedule by thin black lines that end with a small arrowhead so you can see the direction of the line.
On complicated projects with many dependencies, these lines can criss-cross all over the place and make the Gantt chart very difficult to read! That’s why it is a good idea to get your tasks organized in the best possible order before you start adding the links — otherwise you could end up with lines going up and down linking your tasks together.
Without dependencies, all your tasks would start on the same day and you can imagine the chaos that would ensure if that happened. And of course, you can’t start all your tasks on the same day. Let’s use the example of building a shed in your garden to illustrate the 4 different ways to manage dependencies on your project schedule.
1. Finish To Start
The Finish To Start (also known as FS) dependency type is probably the one that appears most on your project schedules. It is the most common, and, in my opinion, the easiest to use as it is the one that appears the most logical. When you are building that shed in your garden, you can’t put the roof on before you build the walls — it’s that sort of dependency. You have to finish Task A (the walls) before you can start Task B (the roof).
Some project management software tools will automatically assume that this is the kind of dependency you want when you add links between tasks on your project schedule. As this is the default option, if you want to choose one of the other types of dependency, you’ll have to change it manually.
2. Finish To Finish
The Finish To Finish type of dependency is often abbreviated to FF. It means that two tasks have to finish at the same time. Task A can’t finish before Task B is completed. This isn’t a very common type of dependency but it is useful to know about it as it can be helpful to link tasks this way on your schedule.
You can use this type of dependency in conjunction with milestones on your project schedule. For example, if the last thing to do on your shed is to hang the birdfeeder from the roof, you could say that the Hang Birdfeeder task has a Finish To Finish dependency with the Shed Complete milestone. In other words, you can’t get to the Shed Complete milestone without making a little feeding station for your garden birds.
3. Start To Start
Start To Start dependencies (often called SS) are pretty much the opposite of Finish To Finish dependencies! It’s the same kind of idea, but in reverse. So, Task A can’t start before Task B starts. In your shed project, we could say that you can’t start the Build Shed task before you complete a task to buy the shed. Buy Shed and Build Shed could have a Start To Start dependency relationship on your project schedule.
Again, this type of dependency is used from time to time, but you’ll still find the Finish To Start type used on far more of your project tasks.
4. Start To Finish
Start To Finish (also known as SF dependencies) relationships between tasks are probably the type that you will use the least. It’s useful to know about them in case they are relevant to your project, but you won’t use them that often.
In a Start To Finish dependency, the start of Task A links to the finish of Task B. In other words, Task B can’t finish before you’ve made a start on Task A. In your build-a-shed project, let’s say that you had to hire a van to move the shed components from the warehouse to your garden.
At the warehouse, the assistant helped you get the parts into the van. However, you can’t unload the van until your brother arrives to help you, as the components are too heavy for one person. In this example, Task A is Unload The Van. Task B is Deliver Shed To Garden. You can’t finish delivering the shed until unloading the van starts.
Start To Finish dependencies are the most complicated to understand and the least used (probably because they are difficult to get your head around). They are often used in construction projects where a task can’t start until another task takes away the resources, like cranes or specialist crew, for them to start work on the next task.
On an IT project, an example would be a handover of a new software product to the operational team. For a while, it’s normal for the project team to provide support for the new system — after all, they built it and they understand how it works.
There will be a period of handover though, and then the operational team will take over managing the support, the project team will be disbanded, and they will start working on other projects. The Close Project task cannot finish before the Handover to Operational Team task has started.
As I said, difficult to get your head around! You can normally manage project scenarios and your schedule by using the other types of dependency, even when you need to plan a handover or use equipment on two tasks.
These are the four ways to manage dependencies on your project schedule: Finish to Start, Finish To Finish, Start To Start and Start To Finish. Now you know what choices are available for linking tasks, you can choose the most appropriate relationships between your tasks for your project activities.
