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جمعه 14 اردیبهشت‌ماه سال 1386

Chapter 4-3:Schedule Development

Schedule Development

Schedule development is the establishment of a start date and a finish date for each of the project activities. Schedule development is where we put together all of the other work from schedule planning. An accurate schedule needs all of the activities, the sequence of those activities, and the length of each activity. With all the work we have done so far, you may think this part should be a piece of cake. In reality, putting together all of the data from the other schedule planning processes and creating a project schedule is one of the more complex processes.

Luckily, you can use a number of different techniques to develop a project schedule. We will talk in detail about three of the most commonly used techniques: critical path method (CPM), duration compression, and the use of project management software.

Project schedule development also includes the use of milestone dates, which mark a significant project event or the end of a project phase.

Let’s get started with the techniques available to develop a schedule.

Schedule Development Techniques

Even though you have a huge pot of data with all of this information about all of the project activities, you still don’t have a schedule. Although it may seem at first that the putting all of the activities together is an unwieldy process, you can use a number of techniques to create a meaningful schedule.

A Guide to the PMBOK lists a number of techniques for schedule development. We will focus on three of the most commonly used schedule development techniques:

  • Mathematical analysis (specifically the critical path method)

  • Duration compression

  • Project management software

Critical Path Method (CPM)

A Guide to the PMBOK defines mathematical analysis as “calculating theoretical early and late start and finish dates for all project activities without regard for any resource pool limitation.” In other words, you are not looking at when any of your resources may be available, but only at when each task can start and end based on dependency relationships with other tasks. A summary of the individual activity time periods provides the project time period.

One of the most widely used mathematical analysis techniques is critical path method (CPM) . The critical path in a project schedule is the longest activity sequence path in the project; therefore, it controls the finish date of the project. The purpose of CPM is to identify this path. The activities on the critical path have no float time . Float is the time a task may be started late or the additional time that can be used to complete the task without impacting project completion. Critical path tasks have zero float, which is why these tasks get so much attention. If a critical path task does not complete as scheduled and no other changes are made, the project end date will be affected.

Note 

Chapter 9, “Project Control” will cover what you can do if you have critical path tasks that are taking longer than planned.

In addition to calculating the overall time to complete the project and identifying tasks on the critical path, CPM provides other useful data. You will be able to determine which tasks can start late or can take longer than planned without impacting the project end date. This information can be used during project execution to help the project manager focus attention on the tasks that have the most impact on the overall project completion date.

We are going to walk through a simple CPM calculation. CPM is rarely done manually, since a variety of software tools will do these calculations for you. But unless you understand the fundamentals behind what the software is doing, you cannot take advantage of what it is telling you.

The network diagram from activity sequencing and the task duration estimates are the key components of the CPM calculation. Refer to the precedence diagram shown in Figure 4.4 as we walk through this example.

Forward Pass  The first step in determining your critical path is to complete a forward pass through the network diagram. This means that you are working from the left to the right of your network diagram. This will give you two calculations for each activity.

Early start is the earliest date an activity may begin as logically constrained by the network. The first activity on the diagram has an early start of 0. Add the duration of that activity to obtain the early finish for that activity. Early finish is the earliest date an activity may finish as logically constrained by the network.

In Figure 4.4, the early start for Task A is 0 since it is the first activity on the network. The duration for A is 3 days, so your early finish will be 3. The early finish for A becomes the early start for its successor, Task B. Continue to calculate the early start and finish dates for each activity on the network moving across the diagram until you reach the box marked “Finish.”

Table 4.1 shows the completed early start and early finish calculations for each of the tasks in our network diagram. Based on the calculations from this completed forward pass, the project can complete on day 20.

Table 4.1: Forward Pass

Task

Early Start

Early Finish

A

0

3

B

3

5

C

3

13

D

5

20

E

13

16

Backward Pass  The next step to complete critical path is to complete a backward pass . This means you start at the finish of your network diagram and work back though each path until you reach start. This gives you two calculations.

Late finish is the latest date an activity can complete without impacting the project end date. Late start is the latest date you can start an activity without impacting the project end date.

In Figure 4.4, the final activity to complete is Task D. The latest it can finish is day 20. To calculate the late start for this activity, subtract the duration of 15 days from the late finish. Your late start is day 5. The late start for Task D becomes the late finish for its predecessor; Task B. Continue back through the network, calculating the late start and late finish for each task on the network diagram.

Then go back and compute the second path starting with Task E. Since the project finish date is day 20, the late finish for Task E is also day 20. By subtracting the duration of 3 days, you obtain the late start of day 17. Continue to calculate the late start and finish dates for each activity on the network.

Table 4.2 shows the completed late start and late finish calculations for our network diagram.

Table 4.2: Backward Pass

Task

Late Start

Late Finish

A

0

3

B

3

5

C

7

17

D

5

20

E

17

20

Float  The final step in determining critical path is to calculate float for each activity on the network diagram. Float is obtained by subtracting the early start from the late start or the early finish from the late finish for each activity. Use the calculations from Tables 4.1 and 4.2 and start with Task A. The early finish is 3 and the late finish is 3, making the float 0. Continue through the network diagram until you have computed the float time for each activity.

Table 4.3 shows the float for each of our tasks.

Table 4.3: Float

Task

Float

A

0

B

0

C

4

D

0

E

4

You are now ready to determine the critical path. Remember we said earlier that the critical path is the path with no float. In our example in Figure 4.4, both Tasks C and E have float, which means they are not on the critical path. A-B-D is the critical path, as each of these tasks has 0 float. If any of the tasks on the critical path do not start on time or take longer than planned, the end date of the project will be impacted; it will not complete within the 20-day estimate. Remember that you must pay particular attention to the status of your critical path tasks over the course of project execution to keep your schedule on track.

Unfortunately, there are times when you complete the network diagram and calculate the critical path and you determine the length of your project is unacceptable to the project stakeholders or does not complete within a mandated legal requirement. If you find yourself in that situation, you need to utilize duration compression techniques.

Duration Compression

You have just learned how to develop a network diagram of your project tasks and lay out your project schedule using CPM. But what happens if your calculation of the total project duration is longer than your target project completion date?

This is where duration compression scheduling techniques come into play. These techniques can be used up front to shorten the planned duration of the project or during project execution to resolve schedule slippage. The two duration compression techniques are crashing and fast track.

Crashing

Crashing is a technique that adds more resources to a task to complete the task more quickly.

Note 

Crashing may have an impact on your budget, so you will need to look at the impacts to both your schedule and your budget.

Warning 

One common misconception regarding adding resources is that if you double the resources, you will cut the duration in half. If two programmers can write the code in 4 weeks, then four programmers can do it in 2 weeks. What happens in the real world may be quite the opposite. Typically, the original resources are initially less productive when you add new resources. The work must be reallocated, which takes time away from the work itself. There may be downtime while the experienced team members train the new members.

There is also the issue of diminishing returns. The more resources that are added, the less impact each resource will make on duration reduction.

Crashing can produce the desired results if used wisely, but it is not the solution for a timeline that is unrealistic based on the scope of the project.

Fast Track

When you fast track a project, you work tasks in parallel that would normally be done in sequence.

For example, suppose that you have a project in which you have to build four servers that are going to interact with one another. You might have initially created four “build server” tasks that were supposed to happen one right after the other. However, when you decide to fast track the project, you’d probably ask the server administrator building the servers if he or she could build all four in approximately the same time. In a fast-track situation, the admin might assemble the server hardware for server one, then start the OS installing. Once that was going he or she might move to assembling Server 2’s hardware and so on. In this way you could shave precious time off of the project.

There is a great deal of risk in fast tracking. If you decide to compress your project schedule using this method, be sure and get input from the team members as to what could go wrong. Document all the risks and present them to your sponsor, your client, and other key stakeholders. Many project managers make the mistake of just trying to do the project faster without any communication as to the impacts on other areas such as quality. You need to make sure that everyone understands the potential consequences. For instance, in the example of the servers above, you can see that the main risk involved is that the admin may get confused as to which step he or she is at in the server-building process and make a critical mistake in bringing up one of the servers.

Project Management Software

Project management software is a wonderful tool that can save you a lot of time. It provides you with the ability to display a number of different views of the project, which can be a great communication tool.

The processes that we have covered in this chapter—activity definition, activity sequence, and schedule development—can all be completed using a project management software package. In fact, you may be wondering why we even bothered to walk through manual examples of these processes, when you can just enter your data in a software package and let it do all the work. In order to effectively use project management software, you must understand the fundamental concepts behind what the software is doing. Otherwise, you will not obtain the full benefit of what the software can provide. Worse yet, you may become frustrated because the way you have entered your tasks causes the software to do things you do not want it to do. Going through each of these processes manually will equip you with the knowledge and understanding to effectively use a software tool.

Keep in mind that even if you will be using software to track the progress of your project, the up-front work that you do as a team to create a WBS and define estimates can still be created manually using a white board and sticky notes. This data can be entered into a software package later for tracking purposes.

If your company provides you with a project management software tool and you have never used one before, ask to attend a class. If that is not possible, try to find someone in your organization who is experienced with the software to give you some on-the-job training.

A good understanding of project management software becomes more important when you start tracking project process, which we will discuss in Chapter 8, “Project Execution.”

Use of one or more of these scheduling techniques will assist the project manager in producing a schedule with a start and end date that accounts for all of the project activities and their dependencies. To make your schedule complete, all that remains is the addition of any required milestone dates.

Milestones

Depending on the specific methodology used and the policies within your organization, you may also need to include milestone dates in your project schedule. A milestone marks a key event in the project life cycle. Typically milestones are included in the project to identify the completion of a major deliverable. If you will be using milestones in your schedule, be sure that all of the activities required to meet the milestone are scheduled to complete before the milestone date.

Some project life cycle methodologies also use milestones to mark the end of one project phase and the beginning of the next phase. Milestones between phases typically have exit or entrance criteria. For example, a system development project milestone for moving from a test phase to a deployment phase could have a list of specific test scenarios that must be successfully completed before the testing phase is complete. This is the exit criterion that must be met before the test phase is considered complete.

Project managers need to pay close attention to milestone dates, as they are also a communication trigger. Stakeholders need to be informed when major deliverables are completed or when a project has successfully moved to a new phase. If these dates are not met, the project manager needs to communicate the current status, plans to bring the project back on track, and the new milestone date. The details of communications planning will be covered in Chapter 6, “Additional Planning Processes.”

Schedule Baseline

The project manager and the project team should review the completed project schedule to address any questions or resolve any outstanding issues. The project team needs to own the schedule and be committed to meeting the planned dates. To facilitate a clear understanding of the schedule, provide each team member with a copy of the schedule to review prior to the meeting. If the project schedule has been developed using a project management software package, you may be able to provide access via a shared folder.

Once the team reviews the project schedule and adds any milestone dates, it is time to establish the schedule baseline, which is a copy of the schedule prior to the start of project work. A baseline is a tool used by the project manager during project execution to monitor and communicate project progress.

The project manager communicates the baseline schedule to the stakeholders. The level of detail provided to the stakeholders will vary depending on the detail each stakeholder requires, but at a minimum cover the key milestone dates

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