In our last post, we demonstrated several different ways of adding a task dependency in Microsoft Project. The default when setting these links is to set up a finish-to-start dependency, so this post will cover how to establish other types of dependencies, as well as how to add lag or lead time, and finally how to determine the correct order for the tasks.
Establishing Other Types of Dependencies
If a finish-to-start task dependency does not accurately reflect the relationship between two tasks, you can use the Task Dependency dialog box to change the dependencies among your tasks. To access the Task Dependency dialog box, simply double-click the dependency link line between the tasks in the Gantt chart.
In the following example, we have decided that in the interest of time the beginning of the task Negotiate new lease would allow the task Finalize drawings to begin, so we want to change the finish-to-start dependency to a start-to-start relationship.
- Double-click the link line between two tasks. In the resulting dialog box, click the down arrow in the Type:. For this example, we linked Negotiate new lease to Finalize drawings and the screen resembles the following:
Figure 1 Task Dependency dialog box
- From the Type: dropdown list, select Start-to-Start (SS) and click OK. The two tasks are now shown to start at the same time. Notice the change in dependency below:
Figure 2 Start-to-Start (SS) task dependency
|Dependencies can also be changed in the Task Details Form (in the split window) by clicking in the Type column for a dependency. They can also be changed in the Task Information dialog box; be sure to work with the successor task, since only the predecessor task(s) are shown in this dialog. Double-click the successor task name to open the Task Information dialog easily.|
Adding Lag or Lead Time to Modify Task Dependencies
In addition to establishing task dependencies, you can specify any necessary delay between tasks by inserting lag. Lag is a required waiting period, generally used to allow something to happen – concrete to set, paint to dry, etc. Lag time lengthens the project duration, but it is logically necessary.
Let’s say we decided we can’t start the Finalize drawings task until some of the Negotiate new lease task is complete. The negotiators feel that they will need at least three days’ discussion before the second task can begin.
- Double-click the link line between the two tasks, then in the Task Dependency dialog box enter “3d” in the Lag.
- Click OK. In the example project, Task 11 now starts 3 days after task 10 starts, as shown below:
Figure 3 Start-to-Start dependency with lag (delay)
Even when tasks are linked finish-to-start, it is not always necessary for the first task to completely finish before the second task can begin. To show that two tasks can overlap, you can specify lead time after establishing a task dependency such as Finish-to-Start. Ultimately, lead time shortens the duration of a project.
Lead time is expressed as a negative number in the lag field.
Determining the Proper Order of Tasks in a Project
The order in which tasks are performed is an important piece of the logic for a project. Often, the starting assumption when entering tasks is that all the detailed tasks will be done on the same day. However, when you look at the detailed task descriptions it is clear that is not the case. Some tasks depend on the outcome of another one. We can visualize a chain of activities each depending on the successful completion of the one before. The sequence is defined using dependencies which link one task as a predecessor with another that is a successor.
Below, we will demonstrate an example of how make a project feasible by determining the proper order for the tasks within it.
- First, identify tasks where the outcome of one task is used directly by another task. In our example project, Decide on venue criteria and Develop list of key agenda items should immediately follow Hold project kick-off meeting. Using the methods discussed earlier in this chapter, link these tasks by establishing two finish-to-start dependencies.
- It is also possible to link several tasks at one time. Select a group of sub-tasks (in the example project, we select Task ID 7 through Task ID 12) and from Task:Schedule click the Link.
- In the same manner, we also linked all the Agenda and schedule sub-tasks (Task IDs 14 to 20). Notice how Hold project kick-off meeting (Task ID 5) now has two successors (Task IDs 7 and 14). Tasks may also have multiple predecessors.
- The WBS structure often becomes even more complicated. Develop list of entertainment events (Task ID 19) is dependent on the venues being considered, and so must be a successor to Perform detailed research on top three potential venues (Task ID 10).
- Because it is necessary for the first five General Planning sub-tasks (Task IDs 6, 13, 21, 22, and 23) to be completed prior to completing the final sub-task, each of these need to be made a predecessor to Present general plan (Task ID 24). All of these changes result in the following:
- Project management typically begins as the project begins, so we create a Start-to-Start dependency between Project Management (Task ID 1) and Hold project kick-off meeting (Task ID 5).