Milestone

A milestone, sometimes called an event, is a significant occurrence in the life of a project. Milestones take no time and consume no resources; they occur instantaneously. Think of them as signposts that signify a point in your trip to project completion. Milestones mark the start or end of one or more activities or the creation of deliverables. (See Chapters 5 and 6 for more on deliverables.) Examples of milestones are draft report approved and design begun.

Activity

An activity, also called a task, is a component of work performed during the course of a project. Activities take time and consume resources; you describe them by using action verbs. Examples of activities are design report and conduct survey.

Make sure you clearly define activities and milestones. The more clearly and granularly you define them, the more accurately you can estimate the time and resources needed to perform them, the more easily you can assign them to someone else, and the more meaningful your reporting of schedule progress becomes.

Duration

Duration is the total number of work periods required to complete an activity. Several factors can affect duration:

• The amount of work effort (the amount of time a person needs to work full time on the activity to complete it) required. See Chapter 8 for details on work effort.
• People’s availability to work on the project.
• Whether multiple people can work on the activity at the same time.
• Capacity of non-personnel resources (for example, a computer’s processing speed and the pages per minute that a copier can print) and their availability.
• Delay. For example, if your manager spends one hour reading your memo after it sat in their inbox for four days and seven hours, the activity’s duration is five days, even though your manager spends only one hour reading it.

The units of time describe two related but different activity characteristics. Duration is the number of work periods required to perform an activity; work effort is the amount of time a person needs to complete the activity. For example, suppose four people have to work together full time for five days to complete an activity. The activity’s duration is five days. The work effort is 20 person-days (4 people times 5 days).

Understanding the basis of a duration estimate helps you figure out ways to reduce it. For example, suppose you estimate that testing a software package requires that it run for 24 hours on a computer. If you can use the computer only six hours in any one day, the duration for your software test is four days. Doubling the number of people working on the test doesn’t reduce the duration to two days, but getting approval to use the computer for 12 hours a day does.

The importance of the critical path

The length of your project’s critical path(s) in your network diagram defines your project’s length (hence, the critical path method for determining your project’s schedule). If you want to finish your project in less time, consider ways to shorten its critical path.

Monitor critical-path activities closely during performance because any delay in critical-path activities delays your project’s completion. Also closely monitor any activities on paths that are close to being critical, because any minor delay on those paths can also delay your project’s completion.

Your project can have two or more critical paths at the same time. In fact, every path in your project can be critical if every one of them takes the same amount of time. However, when every path is critical, you have a high-risk situation; a delay in any activity immediately causes a delay in the completion of the project.

Critical paths can change as your project unfolds. Sometimes activities on a critical path finish so early that the path becomes shorter than one or more other paths that were initially considered noncritical. Other times, activities on an initially noncritical path are delayed to the point where the sum of their completion times becomes greater than the length of the current critical path (which turns the initially noncritical path into a critical one).

The forward pass: Determining critical paths, noncritical paths, and earliest start and finish dates

Your first step in analyzing your project’s network diagram is to start at the beginning and see how quickly you can complete the activities along each path. You should determine this information without taking into account any effects that constraints on the availability of personnel or other resources may have. This start-to-finish analysis is called the forward pass.

To help you understand what a forward pass is, you can perform one through the diagram in Figure 7-2. According to Rule 1, you can consider working on either Activity 1 or Activity 3 (or both together) as soon as the project starts (check out the earlier section “Reading a network diagram” for more info on the two rules of network diagram analysis). First, consider Activities 1 and 2 on the upper path:

• The earliest you can start Activity 1 is right when the project starts (the beginning of week 1).
• The earliest you can finish Activity 1 is the end of week 5 (add Activity 1’s estimated duration of five weeks to its earliest start time, which is the start of the project).
• According to Rule 2, the earliest you can start Activity 2 is the beginning of week 6 because the arrow from Activity 1 is the only one leading to Activity 2.
• The earliest you can finish Activity 2 is the end of week 6 (add Activity 2’s estimated duration of one week to its earliest start time at the beginning of week 6).

So far, so good. Now consider Activities 3 and 4 on the lower path of the diagram:

• The earliest you can start Activity 3 is right when the project starts (the beginning of week 1).
• The earliest you can finish Activity 3 is the end of week 1.
• The earliest you can start Activity 4 is the beginning of week 2.
• The earliest you can finish Activity 4 is the end of week 4.

You have to be careful when you try to determine the earliest you can start Activity 5. According to Rule 2, the two arrows entering Activity 5 indicate you must finish both Activity 1 and Activity 4 before you begin Activity 5. Even though you can finish Activity 4 by the end of week 4, you can’t finish Activity 1 until the end of week 5. Therefore, the earliest you can start Activity 5 is the beginning of week 6.

If two or more activities or milestones lead to the same activity, the earliest you can start that activity is the latest of the earliest finish dates for those preceding activities or milestones.

Is your head spinning yet? Take heart; the end is in sight:

• The earliest you can start Activity 5 is the beginning of week 6.
• The earliest you can finish Activity 5 is the end of week 7.
• The earliest you can finish Activity 2 is the end of week 6. Therefore, the earliest you can finish the entire project (and reach the milestone called Project Ended) is the end of week 7.

So far, you have the following information about your project:

• The length of the critical path (the shortest time in which you can complete the project) is seven weeks. Only one critical path takes seven weeks; it includes the milestone Project Started, Activity 1, Activity 5, and the milestone Project Ended.
• Activity 2, Activity 3, and Activity 4 aren’t on critical paths.

The backward pass: Calculating the latest start and finish dates and slack times

You’re halfway home. In case resource conflicts or unexpected delays prevent you from beginning all the project activities at their earliest possible start times, you want to know how much you can delay the activities along each path and still finish the project at the earliest possible date. This finish-to-start analysis is called the backward pass.

To expand on the example we introduce in the preceding section, the forward pass indicates that the earliest date you can reach the milestone Project Ended is the end of week 7. However, Rule 2 in the earlier section “Reading a network diagram” says you can’t reach the milestone Project Ended until you’ve completed Activities 2 and 5. Therefore, to finish your project by the end of week 7, the latest you can finish Activities 2 and 5 is the end of week 7. Consider the lower path on the diagram in Figure 7-2 with Activities 3, 4, and 5:

• You must start Activity 5 by the beginning of week 6 to finish it by the end of week 7 (because Activity 5’s estimated duration is two weeks).
• According to Rule 2, you can’t start Activity 5 until you finish Activities 1 and 4. So you must finish Activities 1 and 4 by the end of week 5.
• You must start Activity 4 by the beginning of week 3.
• You must finish Activity 3 before you can work on Activity 4. Therefore, you must finish Activity 3 by the end of week 2.
• You must start Activity 3 by the beginning of week 2.

Finally, consider the upper path on the network diagram in Figure 7-2:

• You must start Activity 2 by the beginning of week 7.
• You can’t work on Activity 2 until you finish Activity 1. Therefore, you must finish Activity 1 by the end of week 6.

Be careful in your calculations. You must finish Activity 1 by the end of week 5 to start Activity 5 at the beginning of week 6. But to start work on Activity 2 at the beginning of week 7, you must finish Activity 1 by the end of week 6. So finishing Activity 1 by the end of week 5 satisfies both requirements.

If two or more arrows leave the same activity or milestone, the latest date you can finish the activity or reach the milestone is the earliest of the latest dates that you must start the next activities or reach the next milestones.

In Figure 7-2, the latest start dates for Activities 2 and 5 are the beginnings of week 7 and week 6, respectively. Therefore, the latest date to finish Activity 1 is the end of week 5. The rest is straightforward: You must start Activity 1 by the beginning of week 1 at the latest.

To organize the dates you calculate in the forward and backward passes, consider writing the earliest and latest start dates and the earliest and latest finish dates at the top of each milestone or activity box in the project’s network diagram. Figure 7-3 illustrates how this looks for the example in Figure 7-2.

Now that you have all the earliest and latest start and finish dates for your milestones and activities, you need to determine the slack time for each activity or milestone. You can determine slack time in one of two ways:

• Subtract the earliest possible start date from the latest allowable start date.
• Subtract the earliest possible finish date from the latest allowable finish date.

Thus, you can determine that Activities 2, 3, and 4 have slack times of one week, while Activities 1 and 5 have no slack time. Figure 7-3 displays this information.

If an activity’s slack time is zero, the activity is on a critical path.

Although slack time is defined as the amount of time an activity or milestone can be delayed without delaying your project’s completion date, slack time is actually associated with a path of activities rather than with an individual activity. The information in Figure 7-3 indicates that both Activity 3 and Activity 4 (which are on the same path) have slack times of one week. However, if the start of Activity 3 is delayed by a week to the beginning of week 2, the earliest that Activity 4 can start will be the beginning of week 3, and it will have zero slack time.

A Guide to the Project Management Body of Knowledge, 7th Edition (PMBOK 7) no longer addresses the concept of slack, although prior editions identify the following two types:

• Total slack: The amount of time a schedule activity may be delayed from its earliest start date without delaying the project’s end date or violating a schedule constraint. This is what we refer to as slack.
• Free slack: The amount of time a schedule activity may be delayed without delaying the earliest start date of any immediately following schedule activities or violating a schedule constraint.

As an example of these terms, look at the network diagram in Figure 7-3. Consider that Activity 3 is scheduled to start at its earliest start, or ES (the beginning of week 1), and Activity 4 is scheduled to start at its ES (the beginning of week 2). If you delay the start of Activity 3 by up to one week, you’ll still be able to start Activity 4 at the beginning of week 3 (its LS, or latest start) and end it by the end of week 5, its LF (latest finish). So Activity 3 has a free slack of zero (because delaying its scheduled start date of ES at all will cause the start date of Activity 4 to be delayed), while Activity 4 has a free slack of one week. Coincidently, each activity (3 and 4) has a total slack of one week, since delaying the start of either one by more than one week will delay the completion of the project beyond the current scheduled completion date of the end of week 7.

Note: The concept of total slack is more often used in schedule analyses, and that’s the concept we use in this book. For simplicity, we refer to this information item simply as slack rather than total slack.

Looking at factors that affect predecessors

A predecessor to an activity (Activity A, for example) is an activity or milestone that determines when work on Activity A can begin. PMBOK 7 identifies the following four relationships that can exist between a predecessor and the activity or milestone coming immediately after it (termed its successor):

• Finish-to-start: The predecessor must finish before the successor can start.
• Finish-to-finish: The predecessor must finish before the successor can finish.
• Start-to-start: The predecessor must start before the successor can start.
• Start-to-finish: The predecessor must start before the successor can finish.

The finish-to-start precedence relationship is the one most commonly used, so it’s the one we address in this book. In other words, in this book, a predecessor is an activity that must be completed before its successor activity can start or its successor milestone can be reached.

Sometimes an activity can’t start precisely when its predecessor is finished. A lag is the amount of time after its predecessor is completed that you must wait before an activity can start. A lead is the amount of time before its predecessor is finished that an activity can begin. In this book, we consider only situations where lead and lag times are zero.

An activity is an immediate predecessor to Activity A if you don’t have any other activities between it and Activity A. When you determine the immediate predecessors for every activity, you have all the information you need to draw your project’s network diagram. The following considerations affect the order in which you must perform your project’s activities:

• Mandatory dependencies: These relationships must be observed if project work is to be a success. They include:
  • Legal requirements: Federal, state, and local laws or regulations require that certain activities be done before others. As an example, consider a pharmaceutical company that has developed a new drug in the laboratory and demonstrated its safety and effectiveness in clinical trials. The manufacturer wants to start producing and selling the drug immediately but can’t. Federal law requires that the company obtain Food and Drug Administration (FDA) approval of the drug before selling it.
  • Procedural requirements: Company policies and procedures require that certain activities be done before others. Suppose you’re purchasing new furniture for your company’s offices. You’ve finished selecting and pricing the furniture you want and would like to begin the process of selecting a vendor and placing the order. However, your organization follows a procurement process for large purchases, which requires that the vice president of finance formally approve the expenditure of the funds required before you can proceed.
  • Hard logic: Certain processes must logically occur before others. For example, when building a house, you must pour the concrete for the foundation before you erect the frame.
• Discretionary dependencies: You may choose to establish these relationships between activities, but they aren’t required. They include:
  • Logical dependencies: Performing certain activities before others sometimes seems to make the most sense. Suppose you’re writing a report. Because much of Chapter 3 depends on what you write in Chapter 2, you decide to write Chapter 2 first. You can write Chapter 3 first or work on both at the same time, but that plan increases the chance that you’ll have to rewrite some of Chapter 3 after you finish Chapter 2.
  • Managerial choices: Sometimes you make arbitrary decisions to work on certain activities before others. Consider that you have to perform both Activity C and Activity D. You can’t work on them at the same time, and you know of no legal or logical reason why you should work on one or the other first. You decide to work on Activity C first.
• External dependencies: Starting a project activity may require that certain work external to the project be completed first. For example, imagine that your project includes an activity to test a device you’re developing. You want to start testing right away, but you can’t start this activity until your organization’s test laboratory receives and installs a new piece of test equipment they plan to order.

Choosing immediate predecessors

You can decide on the immediate predecessors for your project’s activities in one of two ways:

• Front-to-back: Start with the activities you can perform as soon as your project begins and work your way through to the end. To use this method, follow these steps:
  1. Select the first activity or activities to perform as soon as your project starts.
  2. Decide which activity or activities you can perform when you finish the first ones (from Step 1).
  3. Continue in this way until you’ve considered all activities in the project.
• Back-to-front: Choose the activity or activities that will be done last on the project and continue backward toward the beginning. To use this method, follow these steps:
  1. Identify the last project activity or activities you’ll conduct.
  2. Decide which activity or activities you must complete right before you can start to work on the last activities (from Step 1).
  3. Continue in this manner until you’ve considered all activities in your project.

Regardless of which method you use to find your project’s immediate predecessors, record the immediate predecessors in a simple table like Table 7-1. (This table lists the immediate predecessors in the example shown in Figure 7-2.)

Determine precedence based on the nature and requirements of the activities, not on the resources you think will be available. Suppose Activities A and B of your project can be performed at the same time but you plan to assign them to the same person. In this case, don’t make Activity A the immediate predecessor for B, thinking that the person can work on only one activity at a time. Instead, let your diagram show that A and B can be done at the same time. Later, if you find out you have another person who can help out with this work, you can evaluate the impact of performing Activities A and B at the same time. (See Chapter 8 for a discussion on how to determine when people are overcommitted and how to resolve these situations.)

When you create your network diagram for simple projects, consider writing the names of your activities and milestones on sticky-back notes and attaching them to chart paper or a wall. For more complex projects, consider using an integrated project management software package. See Chapter 18 for a discussion of how to use software to support your project planning, and check out Microsoft Project 2019 For Dummies by Cynthia Snyder Dionisio (Wiley) for the lowdown on Microsoft Project, the most popular project management software package.

Deciding on the activities

It’s Friday evening, and you and your friend are considering what to do during the weekend to unwind and relax. The forecast for Saturday is for sunny and mild weather, so you decide to go on a picnic at a local lake. Because you want to get the most enjoyment possible from your picnic, you decide to plan the outing carefully by drawing and analyzing a network diagram. Table 7-2 illustrates the seven activities you decide you must perform to prepare for your picnic and get to the lake.

In addition, you agree to observe the following constraints:

• You and your friend will start all activities at your house at 8 a.m. Saturday — you can’t do anything before that time.
• You must perform all seven activities to complete your project.
• You can’t change who must be present during each activity.
• The two lakes you’re considering are in opposite directions from your house, so you must decide where you’re going to have your picnic before you begin your drive.

Setting the order of the activities

Now that you have all your activities listed, you need to decide the order in which you’ll do them. In other words, you need to determine the immediate predecessors for each activity. The following dependencies are required: Your friend must boil the eggs before they can make the egg sandwiches (duh!), and both of you must load the car and decide which lake to visit before you start your drive.

The order of the rest of the activities is up to you. You may consider the following approach:

• Decide which lake before you do anything else.
• After you both agree on the lake, you drive to the bank to get money.
• After you get money from the bank, you get gasoline.
• At the same time, after you agree on the lake, your friend starts to boil the eggs.
• After the eggs are boiled, your friend makes the egg sandwiches.
• After you return with gas and your friend finishes the egg sandwiches, you both load the car.
• After you both load the car, you drive to the lake.

Table 7-3 depicts these predecessor relationships.

Creating the network diagram

Now that you have your immediate predecessors in mind, you can draw the network diagram for your project from the information in Table 7-3.

Observe the following guidelines when drawing your network diagram:

• Begin your diagram with a single milestone (a commonly used name for this milestone is Project Started).
• Clearly specify all conditions that must be met for a milestone to be reached.
• Don’t leave activities or events hanging; have them all come together in a common milestone that represents the end of the project (a commonly used name for this milestone is Project Ended).
• If your network diagram is excessively complex, look for groups of activities that are self-contained (that is, have only each other as predecessors). Define each of these groups as a subproject, where the duration of the subproject is equal to the length of the critical path(s) of the diagram representing the order in which the self-contained activities will be performed.

To create the network diagram for the picnic example, follow these steps:

1. Begin your project with a single milestone and label it Project Started.

2. Find all activities in the table that have no immediate predecessors — they can all start as soon as you begin your project.

   In this case, only Activity 5 has no immediate predecessors.

3. Begin your diagram by drawing the relationship between Project Started and the beginning of Activity 5 (see Figure 7-4).

   Depict Activity 5 with a box and draw an arrow to it from the Project Started box.

4. Find all activities that have your first activity as an immediate predecessor.

   In this case, Table 7-3 shows that Activities 2 and 7 have Activity 5 as an immediate predecessor. Draw boxes to represent these two activities and draw arrows from Activity 5 to Activities 2 and 7 (see Figure 7-5).

5. Continue in the same way with the remaining activities.

   Recognize from Table 7-3 that only Activity 6 has Activity 2 as an immediate predecessor. Therefore, draw a box to represent Activity 6 and draw an arrow from Activity 2 to that box.

   Table 7-3 also shows that only Activity 3 has Activity 7 as an immediate predecessor. So draw a box to represent Activity 3 and draw an arrow from Activity 7 to Activity 3. Figure 7-5 depicts your diagram in progress.

   Now realize that Activity 1 has both Activities 3 and 6 as immediate predecessors. Therefore, draw a box representing Activity 1 and draw arrows from Activities 3 and 6 to this box.

   The rest is pretty straightforward. Because only Activity 4 has Activity 1 as its immediate predecessor, draw a box representing Activity 4 and an arrow from Activity 1 to Activity 4.

6. After adding all the activities to the diagram, draw a box to represent Project Ended and draw an arrow from Activity 4 (the last activity you have to complete) to that box (see Figure 7-6 for the complete network diagram).

Now for the important timing-related questions. First, how long will you and your friend take to get to the lake for your picnic? The upper path (Project Started; Activities 5, 2, 6, 1, and 4; and Project Ended) takes 52 minutes to complete, and the lower path (Project Started; Activities 5, 7, 3, 1, and 4; and Project Ended) takes 57 minutes to complete. Thus, the trip will take 57 minutes from the time you start until you arrive at the lake for your picnic, and the lower path is the critical path.

The second timing-related question you have to answer is whether you can delay any activities and still get to the lake in 57 minutes. If so, which ones can you delay and by how much? To answer these questions, consider the following:

• The network diagram reveals that Activities 5, 7, 3, 1, and 4 are all on the critical path. Therefore, you can’t delay any of them if you want to get to the lake in 57 minutes.
• Activities 2 and 6 aren’t on the critical path, and they can be performed at the same time as Activities 7 and 3. Activities 7 and 3 take 20 minutes to perform, while Activities 2 and 6 take 15 minutes. Therefore, Activities 2 and 6 have a total slack time of 5 minutes.

Performing activities at the same time

One way to shorten the time it takes to do a group of activities is by taking one or more activities off the critical path and doing them in parallel with the remaining activities. However, often you have to be creative to simultaneously perform activities successfully.

Consider the 57-minute solution to the picnic example in Figure 7-6. Assume an ATM is next to the gas station that you use. If you use a full-service gas island, you can get money from the ATM while the attendant fills your gas tank. As illustrated in Figure 7-7, this strategy allows you to perform Activities 2 and 6 at the same time — in a total of ten minutes rather than the 15 minutes you indicated in the initial network diagram.

At first glance, it appears you can cut the total time down to 52 minutes by making this change. But look again. These two activities aren’t on the critical path, so completing them more quickly has no impact on the overall project schedule. (Before you think you can save five minutes by helping your friend make the sandwiches, remember that you agreed you can’t swap jobs.)

Now you have to try again. This time, keep in mind you must reduce the length of the critical path if you want to save time. Here’s another idea: On your drive to the lake, you and your friend are both in the car, but only one of you is driving. The other person is just sitting there. If you agree to drive, your friend can load the fixings for the sandwiches into the car and make the sandwiches while you drive. This adjustment appears to take ten minutes off the critical path. But does it really?

The diagram in Figure 7-6 shows that the upper path (Activities 2 and 6) takes 15 minutes and the lower path (Activities 7 and 3) takes 20 minutes. Because the lower path is the critical path (and the upper path has five minutes of slack), removing up to five minutes from the lower path can reduce the time to complete the overall project by the same amount. However, reducing the lower path by five minutes makes it the same length (15 minutes) as the upper path, which means that both paths are now critical.

Figure 7-8 reveals that taking five more minutes off the lower path (to reflect that the sandwiches take ten minutes to make) doesn’t save more time for the overall project because the upper path still takes 15 minutes. However, removing the extra five minutes from the lower path does give it five minutes of slack.

Now you can consider using your first idea to get money at the ATM while an attendant fills your car with gas. This time, this move can save you five minutes because the upper path is now critical. Figure 7-9 reflects this change in your network diagram.

Finally, you can decide which lake to visit and load the car at the same time, which saves you an additional two minutes. Figure 7-10 illustrates the final 45-minute solution. Note: For clarity, we’ve added to the original list of activities four milestones (Project Started, Project Ended, Ready to load car, and Ready to drive) and two summary activities (related to preparation and travel). We didn’t link either summary activity directly to other project activities, because the subactivities under the two summary activities are already linked to other activities or milestones.

Consider a situation in which you have to complete two or more activities before you can work on two or more new ones. Show this relationship in your diagram by defining a milestone that represents completion of the activities, drawing arrows from the activities to this milestone and then drawing arrows from that milestone to the new activities (refer to Figure 7-9).

In the example, you first complete the activities Get money, Buy gasoline, and Boil eggs, and then you can perform the activities Load car and Decide which lake. You represent this relationship by drawing arrows from each of the first three activities to a newly defined milestone, Ready to load car, and by drawing arrows from that milestone to the activities Load car and Decide which lake.

If you think this analysis is getting complicated, you’re right. You pay a price to perform a group of activities faster. This price includes:

• Increased planning time: You have to precisely detail all the activities and their interrelationships because you can’t afford to make mistakes.
• Increased risks: The list of assumptions grows, increasing the chances that one or more will turn out to be wrong.

In the picnic-at-the-lake example, you make the following assumptions to arrive at a possible 45-minute solution:

• You can get right into the full-service island at a little after 8 a.m.
• Attendants are available to fill up your tank as soon as you pull into the full-service island.
• The ATM is available and working when you pull into the full-service island.
• You and your friend can load the car and make a decision together without getting into an argument that takes an hour to resolve.
• Your friend can make sandwiches in the moving car without totally destroying the car’s interior in the process.

While making assumptions can increase the risk that you may not meet your project schedule, identifying the assumptions you make can improve your ability to increase the chances that they will come true — or at least convince you to develop contingency plans in case they don’t.

Consider your assumption that you can get right into a full-service island at about 8 a.m. on Saturday. You can call the gas station owner and ask whether your assumption is reasonable. If the gas station owner tells you they have no idea how long you’ll have to wait for someone to pump your gas, you may ask them whether paying $200 in cash would make a difference. When they immediately promise to cordon off the full-service island from 7:55 a.m. until 8:20 a.m. and assign two attendants to wait there, one with the nozzle and the other ready to accept your payment (so you’ll be out in ten minutes), you realize you can reduce most uncertainties for a price! Your job is to determine how much you can reduce the uncertainty and what price you have to pay to do so.

When developing schedule options, it’s not your job to preempt someone else from making a decision. Instead, you want to present all options and their associated costs and benefits to the decision-maker so that person can make the best decision. In this instance, you should have told your friend about the helicopter option so they could have considered it when they made the final decision. Of course, to help in their decision-making, you as the PM may be asked for your recommendations.