Allowing for overlap and delays

Although many dependency relationships are relatively clear cut — Task A can begin only when Task B is complete, or Task C can start only after Task B has started — some are more finely delineated. These relationships involve overlap and delay, and these relationships are supported in Microsoft Project by adding lag time or lead time to the dependency relationship.

To understand these two concepts, consider the following examples. Suppose that your project tests a series of metals. In the first task, you apply a solution to the metal, and in the second task, you analyze the results. However, time can be a factor, so you want the analysis to begin only when several days have passed after the application of the solution. You build in a delay between the finish of the first task (the predecessor) and the start of the second (the successor). Figure 4-20 shows a relationship with some lag between the two tasks. The line between the two tasks indicates the dependency, and the space between the bars indicates the gap in time between the finish of one and the start of the next.

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Task Name

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- Phase One Testing

7.5 days

2

Acquire materials

4 days

3

Prepare solutam

i day

m

4

Apply solution

4 hrs

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Complete Analysis

6

- Phase Twn Testing

3 days

7

Acquire malef iols 2

2 days

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8

Prepare solubcri 2

1 day

9

Apply solution 2

6 hrs

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10

Apply heat

2 hrs

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Complete Analysis 2

3 days

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Submit Final Report

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Figure 4-20: After you apply the solution, you must wait four days to analyze the results.

Note You create lag or lead time using the Predecessors tab of the Task Information dialog box. You create lag time by entering a positive duration in the Lag field, and you create lead time by entering a negative duration in the Lag field.

Note Some people prefer to build a task to represent lag rather than to modify a depen dency relationship. For example, instead of placing a dependency between application of the solution and analysis, you can create a three-day-long task called Solution Reaction Period. Then, create a simple dependency relationship between Solution Reaction Period and the analysis so that the analysis task won't begin until Solution Reaction Period is complete. Adding the lag tasks can generate a very long schedule with multiple tasks and relationships to track. But, in a simpler schedule, this approach enables you to see relationships as task bars. You can try both methods and see which works best for you.

Another test in your project involves applying both a solution and heat. You first want to apply the solution for three hours and then begin to apply heat as well. Notice the overlap between the tasks: the predecessor task — applying the solution — begins at 8:00 a.m. and runs to 2:00 p.m. The successor task — applying heat — begins three hours after the start of the predecessor task, at 11:00 a.m. The project shown in Figure 4-21 has some overlap between tasks.

Overlap

Figure 4-21: Some overlap occurs between the application of the solution and the application of the heat in this testing project.

Overlap

Figure 4-21: Some overlap occurs between the application of the solution and the application of the heat in this testing project.

^Note

I set up a task calendar that ignores lunchtime so that both tasks could continue uninterrupted (the icons in the Indicator column represent the task calendar), and I changed the timescale so that you can see the hours of the day.

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