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Activity Planning—From WBS to Project Schedule

  • Plan Schedule Management—6.1
  • Define Activities—6.2
  • Sequence Activities—6.3
  • Estimate Activity Resources—6.4
  • Estimate Activity Durations—6.5
  • Develop Schedule—6.6

The next section of the planning processes address the steps required to develop the project schedule. This is the part of the project plan that might be most familiar to new project managers. Many automated project management tools help create schedules by keeping track of activities, resources, durations, sequencing, and constraints. Although the schedule is an integral part of the project plan, it is only one part. Don’t start working on the schedule until you have a proper WBS. Starting to work before completing the WBS nearly always results in doing more work than is necessary. A good WBS reduces task redundancy and helps ensure that all work performed is in the scope of the project.

Plan Schedule Management

The first process in the time management knowledge area is plan schedule management. This process defines the policies and procedures for planning, managing, and controlling the project schedule. This process provides guidance on how the schedule will be managed throughout the project. All the subsequent processes in the time management knowledge area depend on the plan developed in this process. Table 4.6 shows the inputs, tools and techniques, and outputs for the plan schedule management process.

TABLE 4.6 Plan Schedule Management Inputs, Tools and Techniques, and Outputs

Inputs

Tools and Techniques

Outputs

Project management plan

Expert judgment

Schedule management plan

Project charter

Analytical techniques

Enterprise environmental factors

Meetings

Organizational process assets

Define Activities

The first process in the activity planning section is define activities. This process starts with the WBS and identifies the activities required to produce the various project deliverables. Activities are viewed from the perspective of the work packages. You ask the question, “What activities are required to satisfy this work package requirement?” Next, the resulting information from this process is used to organize the activities into a specific sequence. Table 4.7 shows the inputs, tools and techniques, and outputs for the define activities process.

TABLE 4.7 Define Activities Inputs, Tools and Techniques, and Outputs

Inputs

Tools and Techniques

Outputs

Schedule management plan

Decomposition

Activity list

Scope baseline

Rolling wave planning

Activity attributes

Enterprise environmental factors

Expert judgment

Milestone list

Organizational process assets

Sometimes it is difficult to know everything about a project during the planning stage. It is common to learn more about the project as you work through the project life cycle. This is called progressive elaboration and affects the planning process. If you don’t know everything about a project, you can’t plan the whole project to the necessary level of detail.

For a large project, it is common to plan the entire project at a high level. The project starts with detailed plans in place for the work packages that are near the beginning of the project. As the time draws near to begin additional work, the more detailed, low-level plans for those work packages are added to the project plan. The planning process is revisited multiple times to ensure that the detailed plans contain the latest information known about the project. This practice is called rolling wave planning because the planning wave always moves to stay ahead of the work execution wave.

Sequence Activities

The next process is arranging the activities list from activity definition into a discrete sequence. Some activities can be accomplished at any time throughout the project. Other activities depend on input from another activity or are constrained by time or resources. Any requirement that restricts the start or end time of an activity is a dependency. This process identifies all relationships between activities and notes restrictions imposed by these relationships.

For example, when building a car, you cannot install the engine until the engine has been built and delivered to the main assembly line. This is just one example of how activities can be dependent on one another. The sequence activities process is one that can benefit from the use of computer software to assist in noting and keeping track of inter-activity dependencies. Table 4.8 shows the inputs, tools and techniques, and outputs for the sequence activities process.

TABLE 4.8 Sequence Activities Inputs, Tools and Techniques, and Outputs

Inputs

Tools and Techniques

Outputs

Schedule management plan

Precedence diagramming method (PDM)

Project schedule

Activity list

Dependency determination

Project documents updates

Activity attributes

Leads and lags

Milestone list

Project scope statement

Enterprise environmental factors

Organizational process assets

Network Diagrams

One of the most important topics to understand when planning project activities is how to create network diagrams. A network diagram provides a graphical view of activities and how they are related to one another. The PMP exam tests your ability to recognize and understand the most common type of network diagramming method: the precedence diagramming method (PDM). Make sure you can read a PDM diagram and use the information it presents.

Figure 4.3 shows an example of a PDM diagram.

FIGURE 4.3

FIGURE 4.3 The precedence diagramming method.

Precedence Diagramming Method

A PDM diagram shows nodes—representing activities—connected by arrows that represent dependencies. To represent that activity B is dependent on activity A (in other words, activity A must be complete before activity B starts), simply draw an arrow from A to B. PDM diagrams are also referred to as activity-on-node (AON) diagrams because the nodes contain the activity duration information. (We don’t have enough information to complete all the information presented here yet. We’ll fill in the duration information during activity duration estimating.) In fact, nodes generally contain several pieces of information, including

  • Early start—The earliest date the activity can start
  • Duration—The duration of the activity
  • Early finish—The earliest date the activity can finish
  • Late start—The latest date the activity can start
  • Late finish—The latest date the activity can finish
  • Slack—Difference between the early start and the late start dates

Figure 4.4 shows an example of a PDM node template.

FIGURE 4.4

FIGURE 4.4 The sample PDM node template.

The PDM diagram in Figure 4.3 shows eight activities, labeled A through H, with 13 dependencies. The arrows show how some activities are dependent on other activities. For example, activity B cannot start until activities A and C are complete. To show this dual dependency, we draw an arrow from A to B and another arrow from C to B.

You can represent four types of dependencies with a PDM diagram:

  • Finish-to-start (the most common dependency type)—The successor activity’s start depends on the completion of the predecessor activity.
  • Finish-to-finish—The completion of the successor activity depends on the completion of the predecessor activity.
  • Start-to-start—The start of the successor activity depends on the start of the predecessor activity.
  • Start-to-finish—The completion of the successor activity depends on the start of the predecessor activity.

Project Task Information

When you are comfortable with the main types of network diagrams, you need to understand how to use them. Let’s talk about a few basic scheduling concepts and look at how network diagrams help you understand project schedules, starting with a few project tasks. Table 4.9 lists the tasks for a project, along with the predecessors, duration, and earliest start date.

TABLE 4.9 Project Task Information

Activity

Predecessor

Duration

Earliest Start Date

A

None

5

9/5/14

B

A

2

9/10/14

C

A

3

9/10/14

D

B

7

9/12/14

E

C

4

9/13/14

F

D

1

9/19/14

G

E, F

2

9/20/14

Now use the sample PDM node template shown in Figure 4.4 to create a PDM diagram for the project.

Your completed network diagram should look like the one shown in Figure 4.5.

FIGURE 4.5

FIGURE 4.5 A completed sample PDM diagram.

Estimate Activity Resources

Now you have a list of activities and their relative dependencies. The next process is to associate activities with the resources required to accomplish the work. This process involves listing each type and amount, or quantity, of each required resource. Every activity requires resources of some sort. Activity resources can include

  • People
  • Equipment
  • Materials and supplies
  • Money

Table 4.10 shows the inputs, tools and techniques, and outputs for the estimate activity resources process.

TABLE 4.10 Estimate Activity Resources Inputs, Tools and Techniques, and Outputs

Inputs

Tools and Techniques

Outputs

Schedule management plan

Expert judgment

Activity resource requirements

Activity list

Alternative analysis

Resource breakdown structure

Activity attributes

Published estimating data

Project documents updates

Resource calendars

Bottom-up estimating

Risk register

Project management software

Activity cost estimates

Enterprise environmental factors

Organizational process assets

Two of the tools and techniques warrant further discussion. One of the techniques you use when estimating activity resources is alternative analysis. Analyzing the various alternatives provides an opportunity to consider other sources or ways to achieve the desired result for an activity. Alternatives might be more desirable than the initial expected approach due to cost savings, higher quality, or earlier completion. Another important outcome of alternative analysis is that in case the primary source becomes unavailable, you might have already identified a replacement method to complete the work. Suppose your main supplier of industrial fittings suffers a catastrophic fire. If your alternative analysis identified another source, you might be able to continue the project with minimal disruption.

The second item is bottom-up estimating. Recall that one of the purposes of creating the WBS is to decompose project work into work packages that are small enough to reliably estimate for duration and resource requirements. Using the WBS, you can provide estimates for mid- and high-level work by aggregating the estimates for the work packages that make up the desired work. Because this process starts at the lowest level of work (the work package) to create the estimate, it is called bottom-up estimating. This type of estimating tends to be fairly accurate because the estimates come from the people doing the actual work. The alternative is top-down estimating. Top-down estimates generally come from management or a source that is higher up than the people actually doing the work. The estimates are really educated guesses on the amount of resources required for a collection of work packages and tend to be less reliable than bottom-up estimates.

Estimate Activity Durations

After the resource estimates are established for each of the activities, it’s time to assign duration estimates. The estimate activity durations process approximates the number of work periods that are needed to complete scheduled activities. Each estimate assumes that the necessary resources are available to be applied to the work package when needed. Table 4.11 shows the inputs, tools and techniques, and outputs for the activity duration estimating process.

TABLE 4.11 Estimate Activity Duration Inputs, Tools and Techniques, and Outputs

Inputs

Tools and Techniques

Outputs

Schedule management plan

Expert judgment

Activity duration estimates

Activity list

Analogous estimating

Project documents updates

Activity attributes

Parametric estimating

Activity resource requirements

Three-point estimating

Resource calendars

Group decision-making techniques

Project scope statement

Reserve analysis

Risk register

Resource breakdown structure

Enterprise environmental factors

Organizational process assets

In addition to expert judgment and reserve analysis, four main techniques are used for project activity duration estimation. In many cases, using multiple techniques provides more accurate estimates. The four estimation techniques are

  • Analogous estimating—This uses actual duration figures from similar activities. These activities can be from the same project or another project but share similarities in budget, size, weight, complexity, or other parameters.
  • Parametric estimating—This calculates duration estimates by multiplying the quantity of work by the productivity rate. This type of estimate works best for standardized, and often repetitive, activities.
  • Three-point estimates—This uses three estimate values for each activity:

    • Most likely (t M)—The duration most likely to occur.
    • Optimistic (t O)—The duration of the activity based on the best-case scenario.
    • Pessimistic (t P)—The duration of the activity based on the worst-case scenario.

    This approach originated with the Program Evaluation and Review Technique (PERT). PERT analysis calculates the expected (tE) activity from the three-point estimates by using the following formula:

    tE = (tO + 4 * tM + tP) / 6
  • Triangular distribution—This simple estimating method takes an average of the most likely, optimistic, and pessimistic values. Unlike a three-point estimate, each value receives the same weight. This estimating method assumes that risks are just as likely to be realized as the most likely estimate. You can calculate a triangular distribution by using the following formula:

    Average = (tO + tM + tP) / 3

Develop Schedule

The next step is to develop the actual project schedule. The develop schedule process pulls all the activity information together and results in the project’s initial (baseline) schedule. As work is iteratively planned and accomplished and the project moves through its life cycle, changes to the schedule are likely to occur. The schedule is a dynamic document and requires constant attention on the part of the project manager to ensure that the project stays on track. Table 4.12 shows the inputs, tools and techniques, and outputs for the develop schedule process.

TABLE 4.12 Develop Schedule Inputs, Tools and Techniques, and Outputs

Inputs

Tools and Techniques

Outputs

Schedule management plan

Schedule network analysis

Schedule baseline

Activity list

Critical path method

Project schedule

Activity attributes

Critical chain method

Schedule data

Project schedule network diagrams

Resource optimization techniques

Project calendars

Activity resource requirements

Modeling techniques

Project management plan updates

Resource calendars

Leads and lags

Project documents updates

Activity duration estimates

Schedule compression

Project scope statement

Scheduling tool

Risk register

Project staff assignments

Resource breakdown structure

Enterprise environmental factors

Organizational process assets

An important topic to understand with respect to project schedules is the critical path. In the AON diagram in Figure 4.3, the critical path is the longest path from start to finish. It is calculated by adding all the durations along each path from start to finish. The reason it is called the critical path is that any delay (or increase in duration) of any activity on the critical path causes a delay in the project. It is critical that all activities on this path be completed on schedule.

Critical Path

Using the network diagram in Figure 4.5, you can calculate the project critical path. The critical path is the route with the longest total duration. The critical path method performs a forward and backward pass through the schedule network, calculating the early start and finish dates and the late start and finish dates for all activities, based on durations and relationships. The critical path method does not take into account resource limitations. The critical chain method does consider resource limitations. In short, the critical chain method uses the critical path method output and modifies the schedule network to account for limited resources. In this example, there are two routes from Task A to Task G:

  • Path A–B–D–F–G will take 17 days to complete. (Just add up all the durations: 5 + 2 + 7 + 1 + 2 = 17)
  • Path A–C–E–G will take 14 days to complete.

From this diagram, you can see that the longest path is A–B–D–F–G, and that is the critical path. Any delays in any of these tasks delay the project.

Float

The PDM diagram in Figure 4.5 has several pieces of information filled in for each node that we have not discussed. The task name and duration are self-explanatory. What about the rest of the information? The main task of developing the project schedule is to relate each of the tasks and combine duration, resource requirements, and dependencies. You need to make several passes through the network diagram to calculate the values necessary to create a project schedule.

In general, you make two main passes through each path in your network diagram. The first pass starts with the initial project task (the project start task). A task’s early start date is the earliest you can start working on that task. The late start date is the latest you can start working on the task. The difference between the early and late start dates is called float. The float is the schedule flexibility of a task. In Figure 4.5, the early start date for Task A is 9/5/14. To get the early finish date, just add the duration to the early start date. The duration for Task A is 5 days, so the earliest Task A can finish is 9/10/14. Now, the early finish date for Task A becomes the early start date for any tasks that are dependent on Task A (namely, Task B and Task C). Then, continue to follow each path until you reach the final task, calculating the new early end dates by adding the duration to the early start dates.

Now it is time for the second pass through your project to calculate the late start and late ending dates. This pass starts at the end and moves backward through the same paths you just followed in the forward pass. The first step in the backward pass is to record the late ending date. It is the same as the early ending date for the last task in the project. Then, subtract the duration to get the late start date. In Figure 4.5, the late ending date for Task G is 9/22/14, and the late start date is 9/20/14. Next, move backward to each task on which your current task depends (that is each task that has an arrow pointing to your current task). The late ending date for this predecessor task is the same as the late start date of the dependent task. In other words, the late ending date for Task F and Task E would be 9/20/14 (the late start date for Task G). Continue backward through the project, subtracting the duration to calculate a new late start date.

After completing both the forward and backward passes, you should have all of the early start times (EST), early finish times (EFT), late start times (LST), and late finish times (LFT) filled in. To complete the network diagram entries, calculate the float for each task by subtracting the early start date from the late start date. The float is the amount of time each task can be delayed without delaying the project.

Finally, add the durations for each path from the start task to the finish task. The largest total represents the critical path of your project. There could be more than one critical path. Remember that tasks on the critical path all have a float of 0, and any delay of a task on the critical path results in an overall project delay.

Allocating Resources

In addition to calculating the critical path and critical chain, it might be necessary to address resource limitations. The process of reallocating resources that have been overallocated is called resource leveling. This technique seeks to avoid work stoppage due to limited resources being required by multiple activities. Remember that resource leveling can often change the critical path. Because resource allocation can change the critical path it is often useful to implement another technique: what-if scenarios. A what-if scenario allows the project planners to explore the effect to the critical path of resource availability changes. For example, if you depend on a particular person to complete work on the critical path, what happens if that person becomes ill? Such a question would be part of a what-if scenario.

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