A predecessor defines a relationship between two tasks in time. There are many different ways to interpret the relationship depending upon your point of view, but they are all represented by the same ball-and-socket connection in Gantto. The arrow below points to a predecessor linking Task A to Task B: predecessor2 Task Dependencies These connections can be interpreted in different ways depending on you point of view:
  • The following task (B) should start when the preceding task (A) finishes
  • The following task (B) depends upon the preceding task (A) being complete
  • The two tasks are constrained such that the end of task A is the same as the beginning of task B
These task dependencies are one of the key features that elevate a Gantt Chart above a drawing or a spread sheet because they represent represent task relationships that are independent of the position on the screen or the start and end dates of the tasks. For in stance in the toy example above, if I learn that Task A will take twice as long as I originally expected, I can immediately see that impact on Task B and the rest of the project. While this is modestly useful for this simple example, often a project model can have tens or hundreds of dependencies which are all maintained automatically by the Gantt Chart. predecessor3 Task Dependencies One thing that might be confusing initially is that the two tasks shown here are separated by a weekend. In this case the following task starts at the next available working time after 5pm on Friday which is 8am Monday morning.

Adding Predecessors With a Mouse

There are several ways to add dependencies to your schedules. To build a schedule forward in time you can simply drag the round handle at the end of the preceding task dependencies1 Task Dependencies To the body of the following task: dependencies2 Task Dependencies Which creates a dependency between the end of the preceding task to the beginning of the following task. This also move the following task so that its start time now matches the end time of the preceding task. dependencies3 Task Dependencies To remove a dependency, click one of the two balls on either side of the dependency dependencies4 Task Dependencies One neat feature unique to Gantto is that we explicitly account for building schedules backward in time beginning with a fixed end date. This kind of scheduling exercise is useful whenever a team is working to a deadline. The workflow is very similar to building a schedule forward in time, first you select the round handle at the beginning of the following task: dependencies5 Task Dependencies Then drag it onto the task that you want to precede this one: dependencies6 Task Dependencies And the constraint is made while moving the preceding task back so that its end date matches the following task’s start date: dependencies7 Task Dependencies

Dependency Limitations

Dependencies are a very helpful feature of Gantt Charts, but they do have limitations. For instance, it is not possible to make the “new task” in this situation a predecessor of Task A dependencies8 Task Dependencies And Gantto lets you know this by coloring the dependency grey instead of green which is used for valid dependencies.

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