page 168
CHAPTER
SIX
6
Developing a Project Schedule
page 169
I keep six honest serving-men (they taught me all I knew); their names are What and Why and When and How and Where and Who.
—Rudyard Kipling
6.1 Developing the Project Network
The project network is the tool used for planning, scheduling, and monitoring project progress. The network is developed from the information collected for the WBS and is a graphic flow chart of the project job plan. The network depicts the project activities that must be completed, the logical sequences, the interdependencies of the activities to be completed, and in most cases the times for the activities to start and finish along with the longest path(s) through the network—the critical path. The network is the framework for the project information system that will be used by the project managers to make decisions concerning project time, cost, and performance.
Developing the project networks takes time for someone or some group to develop; therefore, they cost money! Are networks really worth the struggle? The answer is page 170definitely yes, except in cases where the project is considered trivial or very short in duration.1 The network is easily understood by others because the network presents a graphic display of the flow and sequence of work through the project. Once the network is developed, it is very easy to modify when unexpected events occur as the project progresses. For example, if materials for an activity are delayed, the impact can be quickly assessed and the whole project revised in only a few minutes with the computer. These revisions can be communicated to all project participants quickly (for example, via e-mail or project website).
The project network provides other invaluable information and insights. It provides the basis for scheduling labor and equipment. It enhances communication that melds all managers and groups together in meeting the time, cost, and performance objectives of the project. It provides an estimate of project duration rather than picking a random project completion date or someone’s preferred date. The network gives the times when activities can start and finish and when they can be delayed. It provides the basis for budgeting the cash flow of the project. It identifies which activities are “critical” and, therefore, should not be delayed if the project is to be completed as planned. It highlights which activities to consider if the project needs to be compressed to meet a deadline.
There are other reasons project networks are worth their weight in gold. Basically project networks minimize surprises by getting the plan out early and allowing corrective feedback. A commonly heard statement from practitioners is that the project network represents three-quarters of the planning process. Perhaps this is an exaggeration, but it signals the perceived importance of the network to project managers in the field.
6.2 From Work Package to Network
Project networks are developed from the WBS. The project network is a visual flow diagram of the sequence, interrelationships, and dependencies of all the activities that must be accomplished to complete the project. An activity is an element in the project that consumes time—for example, work or waiting. Work packages from the WBS are used to build the activities found in the project network. An activity can include one or more work packages. The activities are placed in a sequence that provides for orderly completion of the project. Networks are built using nodes (boxes) and arrows (lines).
Integrating the work packages and the network represents a point where the management process often fails in practice. The primary explanations for this failure are that (1) different groups (people) are used to define work packages and activities and (2) the WBS is poorly constructed and not deliverable/output oriented. Integration of the WBS and project network is crucial to effective project management. The project manager must be careful to guarantee continuity by having some of the same people who defined the WBS and work packages develop the network activities.
Networks provide the project schedule by identifying dependencies, sequencing, and timing of activities, which the WBS is not designed to do. The primary inputs for developing a project network plan are work packages. Remember, a work package is defined independently of other work packages, has definite start and finish points, requires specific resources, includes technical specifications, and has cost estimates for the package. However, dependency, sequencing, and timing of each of these factors are not included in the work package. A network activity can include one or more work packages.
page 171
Figure 6.1 shows a segment of the WBS example and how the information is used to develop a project network. The lowest-level deliverable in Figure 6.1 is “circuit board.” The cost accounts (design, production, test, software) denote project work, organization unit responsible, and time-phased budgets for the work packages. Each cost account represents one or more work packages. For example, the design cost account has two work packages (D-1-1 and D-1-2)—specifications and documentation. The software and production accounts also have two work packages. Developing a network requires sequencing tasks from all work packages that have measurable work.
FIGURE 6.1
WBS/Work Packages to Network
Figure 6.1 traces how work packages are used to develop a project network. You can trace the use of work packages by the coding scheme. For example, activity A uses work packages D-1-1 and D-1-2 (specifications and documentation), while activity C page 172uses work package S-22-1. This methodology of selecting work packages to describe activities is used to develop the project network, which sequences and times project activities. Care must be taken to include all work packages. The manager derives activity time estimates from the task times in the work package. For example, activity B (proto 1) requires five weeks to complete; activity K (test) requires three weeks to complete. After computing the activity early times and late times, the manager can schedule resources and time-phase budgets (with dates).
6.3 Constructing a Project Network
Terminology
Every field has its jargon that allows colleagues to communicate comfortably with each other about the techniques they use. Project managers are no exception. Here are some terms used in building project networks:
Activity. For project managers, an activity is an element of the project that requires time. It may or may not require resources. Typically an activity consumes time—either while people work or while people wait. Examples of the latter are time waiting for contracts to be signed, materials to arrive, drug approval by the government and budget clearance. Activities usually represent one or more tasks from a work package. Descriptions of activities should use a verb/noun format—for example, develop product specifications.
Parallel activities. These are activities that can take place at the same time, if the manager wishes. However, the manager may choose to have parallel activities not occur simultaneously.
Burst activity. This activity has more than one activity immediately following it (more than one dependency arrow flowing from it).
Merge activity. This is an activity that has more than one activity immediately preceding it (more than one dependency arrow flowing to it).
Path. This is a sequence of connected, dependent activities.
Critical path. When this term is used, it means the path(s) with the longest duration through the network; if an activity on the path is delayed, the project is delayed the same amount of time.
Basic Rules to Follow in Developing Project Networks
The following eight rules apply in general when developing a project network:
Networks flow typically from left to right.
An activity cannot begin until all preceding connected activities have been completed.
Arrows on networks indicate precedence and flow. Arrows can cross over each other.
Each activity should have a unique identification number.
An activity identification number must be larger than that of any activities that precede it.
Looping is not allowed (in other words, recycling through a set of activities cannot take place).
Conditional statements are not allowed (that is, this type of statement should not appear: if successful, do something; if not, do nothing).
Experience suggests that when there are multiple starts, a common start node can be used to indicate a clear project beginning on the network. Similarly, a single project end node can be used to indicate a clear ending.
page 173
Read Snapshot from Practice 6.1: The Yellow Sticky Approach to see how these rules are used to create project networks.
6.4 Activity-on-Node (AON) Fundamentals
Historically, two methods have been used to develop project networks: activity-on-node (AON) and activity-on-arrow (AOA). Over time the availability of advanced computer graphics improved the clarity and visual appeal of the AON method. Today the activity-on-node method has come to dominate nearly all project network plans. For this reason, we have limited our discussion to AON methods. Figure 6.2 shows a few typical uses of building blocks for the AON network construction. An activity is represented by a node (box). The node can take many forms, but in recent years the node represented as a rectangle (box) has dominated. The dependencies among activities are depicted by arrows between the rectangles (boxes) on the AON network. The arrows indicate how the activities are related and the sequence in which things must be accomplished. The length and slope of the arrow are arbitrary and set for the convenience of drawing the network. The letters in the boxes serve here to identify the activities while you learn the fundamentals of network construction and analysis. In practice, activities have identification numbers and descriptions.
page 174
FIGURE 6.2
Activity-on-Node Network Fundamentals
There are three basic relationships that must be established for activities included in a project network. The relationships can be found by answering the following three questions for each activity.
Which activities must be completed immediately before this activity? These activities are called predecessor activities.
Which activities must immediately follow this activity? These activities are called successor activities.
Which activities can occur while this activity is taking place? This is known as a concurrent or parallel relationship.
Sometimes a manager can use only questions 1 and 3 to establish relationships. This information allows the network analyst to construct a graphic flow chart of the sequence and logical interdependencies of project activities.
Figure 6.2A is analogous to a list of things to do where you complete the task at the top of the list first and then move to the second task, etc. This figure tells the project manager that activity A must be completed before activity B can begin and that activity B must be completed before activity C can begin.
Figure 6.2B tells the project manager that activities Y and Z cannot begin until activity X is completed. This figure also indicates that activities Y and Z can occur page 175concurrently or simultaneously if the project manager wishes; however, it is not a necessary condition. For example, pouring a concrete driveway (activity Y) can take place while landscape planting (activity Z) is being accomplished, but land clearing (activity X) must be completed before activities Y and Z can start. Activities Y and Z are considered parallel activities. Parallel paths allow concurrent effort, which may shorten the time to do a series of activities. Activity X is sometimes referred to as a burst activity because more than one arrow bursts from the node. The number of arrows indicates how many activities immediately follow activity X.
Figure 6.2C shows the project manager that activities J, K, and L can occur simultaneously if desired and that activity M cannot begin until activities J, K, and L are all completed. Activities J, K, and L are parallel activities. Activity M is called a merge activity because more than one activity must be completed before M can begin. Activity M could also be called a milestone—a significant accomplishment.
In Figure 6.2D, activities X and Y are parallel activities that can take place at the same time; activities Z and AA are also parallel activities. But activities Z and AA cannot begin until activities X and Y are both completed. Given these fundamentals of AON, we can practice developing a simple network. Remember, the arrows can cross over each other (e.g., Figure 6.2D), be bent, or be any length or slope. Neatness is not a criterion for a valid, useful network—only accurate inclusion of all project activities, their dependencies, and their time estimates.
Information for a simplified project network is given in Table 6.1. This project represents a new automated warehouse system for picking frozen food package orders and moving them to a staging area for delivery to stores.
TABLE 6.1
Network Information
| AUTOMATED WAREHOUSE Order Picking System |
||
| Activity | Description | Preceding Activity |
| A | Define Requirements | None |
| B | Assign Team | A |
| C | Design Hardware | A |
| D | Code Software | B |
| E | Build and Test Hardware | C |
| F | Develop Patent Request | C |
| G | Test Software | D |
| H | Integrate Systems | E, F, G |
Figure 6.3 shows the first steps in constructing the AON project network from the information in Table 6.1. We see that activity A (Define Requirements) has nothing preceding it; therefore, it is the first node to be drawn. Next, we note that activities B (Assign Team) and C (Design Hardware) are both preceded by activity A. We draw two arrows and connect them to activities B and C. This segment shows the project manager that activity A must be completed before activities B and C can begin. After A is completed, B and C can take place concurrently, if desired. Figure 6.4 shows the completed network with all of the activities’ sequences and dependencies.
FIGURE 6.3
Automated Warehouse—Partial Network
FIGURE 6.4 Automated Warehouse—Completed Network
The information in Figure 6.4 is tremendously valuable to those managing the project. However, estimating the duration for each activity will further increase the value of the network. A realistic project plan and schedule require reliable time estimates for project activities. The addition of time to the network allows us to estimate how long the project will take. When activities can or must start, when resources must be available, which activities can be delayed, and when the project is estimated to be page 176complete are all determined from the times assigned. Deriving an activity time estimate necessitates early assessment of resource needs in terms of material, equipment, and people. In essence, the project network with activity time estimates links the planning, scheduling, and controlling of projects.
6.5 Network Computation Process
Drawing the project network places the activities in the right sequence for computing the start and finish times of activities. Activity time estimates are taken from the task times in the work package and added to the network (review Figure 6.1). Performing a few simple computations allows the project manager to complete a process known as the forward and backward pass. Completion of the forward and backward pass will answer the following questions.
page 177
Forward Pass—Earliest Times
How soon can the activity start (early start—ES)?
How soon can the activity finish (early finish—EF)?
How soon can the project be finished (expected time—TE)?
Backward Pass—Latest Times
How late can the activity start (late start—LS)?
How late can the activity finish (late finish—LF)?
Which activities represent the critical path (CP)? This is the longest path in the network, which, when delayed, will delay the project.
How long can the activity be delayed (slack or float—SL)?
The terms in parentheses represent the acronyms used in most texts and computer programs and by project managers. The forward and backward pass process is presented next.
Forward Pass—Earliest Times
The forward pass starts with the first project activity(ies) and traces each path (chain of sequential activities) through the network to the last project activity(ies). As you trace along the path, you add the activity times. The longest path denotes the project completion time for the plan and is called the critical path (CP). Table 6.2 lists the activity times in workdays for the Automated Warehouse project example we used for drawing a network.
TABLE 6.2 Network Information
| AUTOMATED WAREHOUSE Order Picking System |
|||
| Activity | Description | Preceding Activity | Activity Time |
| A | Define Requirements | None | 10 workdays |
| B | Assign Team | A | 5 |
| C | Design Hardware | A | 25 |
| D | Code Software | B | 20 |
| E | Build & Test Hardware | C | 50 |
| F | Develop Patent Request | C | 15 |
| G | Test Software | D | 35 |
| H | Integrate Systems | E, F, G | 15 |
Figure 6.5 shows the network with the activity time estimate found in the node (see “DUR” for duration in the legend). For example, activity A (Define Requirements) has an activity duration of 10 workdays, and activity E (Build & Test Hardware) has a duration of 50 days. The forward pass begins with the project start time, which is usually time zero. (Note: Calendar times can be computed for the project later in the planning phase.)
FIGURE 6.5 Activity-on-Node Network
In our Automated Warehouse example, the early start time for the first activity (activity A) is zero. This time is found in the upper left corner of the activity A node in Figure 6.6. The early finish for activity A is 10 days (EF = ES + DUR, or 0 + 10 = 10). Next we see that activity A is the predecessor for activities B (Assign Team) and C (Design Hardware). Therefore the earliest activities B and C can begin is the instant in time when activity A is completed; this time is 10 days. You can now page 178see in Figure 6.6 that activities B and C have an early start (ES) of 10 days. Using the formula EF = ES + DUR, the early finish (EF) times for activities B and C are 15 and 35 days. Following the same process of moving along each network path, the early start and finish times for selected activities are shown here:
FIGURE 6.6 Activity-on-Node Network Forward Pass
page 179
| Activity D: ES = 15 | EF = 15 + 20 = 35 | Activity F: ES = 35 | EF = 35 + 15 = 50 |
| Activity E: ES = 35 | EF = 35 + 50 = 85 | Activity G: ES = 35 | EF = 35 + 35 = 70 |
Activity H (Integrate Systems) is a merge activity because it is preceded by more than one activity. The early start (ES) of a merge activity depends on the early finish (EF) of all activities that merge to it. In this project, activity H is preceded by activities E, F, and G. Which activity controls the ES of activity H? The answer is activity E. In Figure 6.6 the EF times are 85, 50, and 70. Since 85 days is the largest EF time, activity E controls the ES for activity H, which is 85. If activity E is delayed, activity H will be delayed. The early finish for activity H or the project is 100 days (EF = ES + DUR, or 85 + 15 = 100).
The forward pass requires that you remember just three things when computing early activity times:
You add activity times along each path in the network (ES + DUR = EF).
You carry the early finish (EF) to the next activity where it becomes its early start (ES), or
If the next succeeding activity is a merge activity, you select the largest early finish number (EF) of all its immediate predecessor activities.
The three questions derived from the forward pass have been answered; that is, early start (ES), early finish (EF), and the project expected duration (TE) times have been computed. The backward pass is the next process to learn.
Backward Pass—Latest Times
The backward pass starts with the last project activity(ies) on the network. You trace backward on each path, subtracting activity times to find the late start (LS) and late finish (LF) times for each activity. Before the backward pass can be computed, the late finish for the last project activity(ies) must be selected. In early planning stages this time is usually set equal to the early finish (EF) of the last project activity (or in the case of multiple finish activities, the activity with the largest EF). In some cases an imposed project duration deadline exists, and this date will be used. Let us assume for planning purposes we can accept the EF project duration (TE) equal to 100 workdays. The LF for activity H becomes 100 days (EF = LF) (see Figure 6.7).
FIGURE 6.7 Activity-on-Node Network Backward Pass
The backward pass is similar to the forward pass; you need to remember three things:
You subtract activity times along each path starting with the project end activity (LF − DUR = LS).
You carry the LS to the preceding activity to establish its LF, or
If the next preceding activity is a burst activity; in this case you select the smallest LS of all its immediate successor activities to establish its LF.
Let us apply these rules to our Automated Warehouse example. Beginning with activity H (Integrate Systems) and an LF of 100 workdays, the LS for activity H is 85 days (LF − DUR = LS, or 100 − 15 = 85). The LS for activity H becomes the LF for page 180activities E, F, and G. Moving backward on the network, the late starts for E, F, and G are shown here (LS = LF − DUR):
| Activity E: LS = 85 − 50 = 35 | Activity G: 85 − 35 = 50 |
| Activity F: LS = 85 − 15 = 70 |
At this point we see that activity C is a burst activity that ties to (precedes) activities E and F. The late finish for activity C is controlled by the LS of activities E and F. The smallest LS of activities E and F (LS’s = 35 and 70) is activity E. This establishes the LF for activity C. The LS for activity C becomes 10. Moving backward to the first project activity, we note it is also a burst activity that links to activities B and C. The LF of activity A is controlled by activity C, which has the smallest LS of 10 days. Given an LF of 10 days, the LS for activity is time period zero (LS = 10 − 10 = 0). The backward pass is complete, and the latest activity times are known. Figure 6.8 shows the completed network with all the early, late, and slack times included. Slack can be important to managing your project.
FIGURE 6.8 Forward and Backward Pass Completed with Slack Times
Determining Slack (or Float)
Total Slack
When the forward and backward pass has been computed, it is possible to determine which activities can be delayed by computing “slack,” or “float.” Total slack tells us the amount of time an activity can be delayed and not delay the project. Stated page 181differently, total slack is the amount of time an activity can exceed its early finish date without affecting the project end date or an imposed completion date.
Total slack, or float, for an activity is simply the difference between the LS and ES (LS − ES = SL) or between the LF and EF (LF − EF = SL). For example, in Figure 6.8 the total slack for activity D is 15 workdays, for activity F is 35 days, and for activity E is zero. If total slack of one activity in a path is used, the ES for all activities that follow in the chain will be delayed and their slack reduced. Use of total slack must be coordinated with all participants in the activities that follow in the chain.
After slack for each activity is computed, the critical path(s) is (are) easily identified. When the LF = EF for the end project activity, the critical path can be identified as those activities that also have LF = EF or a slack of zero (LF − EF = 0 or LS − ES = 0). The critical path is the network path(s) that has (have) the least slack in common. This awkward arrangement of words is necessary because a problem arises when the project finish activity has an LF that differs from the EF found in the forward pass—for example, an imposed duration date. If this is the case, the slack on the critical path will not be zero; it will be the difference between the project EF and the imposed LF of the last project activity. For example, if the EF for the project is 100 days, but the imposed LF or target date is set at 95 days, all activities on the critical path have a slack of minus 5 days. Of course, this would result in a late start 5 days for the first project activity—a good trick if the project is to start now. Negative slack occurs in practice when the critical path is delayed.
In Figure 6.8 the critical path is marked with dashed arrows—activities A, C, E, and H. Delay of any of these activities will delay the total project by the same number of days. Since actual projects may have many critical activities with numerous preceding dependencies, coordination among those responsible for critical activities is crucial. Critical activities typically represent about 10 percent of the activities of the project. Therefore project managers pay close attention to the critical path activities to be sure they are not delayed. See Snapshot from Practice 6.2: The Critical Path.
page 182
We use the term sensitivity to reflect the likelihood the original critical path(s) will change once the project is initiated. Sensitivity is a function of the number of critical or near-critical paths. A network schedule that has only one critical path and noncritical activities that enjoy significant slack would be labeled insensitive. Conversely a sensitive network would be one with more than one critical path and/or noncritical activities with very little slack. Under these circumstances the original critical path is much more likely to change once work gets under way on the project. How sensitive is the Automated Warehouse schedule? Not very, since there is only one critical path and the two other noncritical paths have 15 and 35 days of slack, which suggests considerable flexibility. Project managers assess the sensitivity of their network schedules to determine how much attention they should devote to managing the critical path.
Free Slack (Float)
Free slack (FS) is unique. It is the amount of time an activity can be delayed without delaying any immediately following (successor) activity. Or free slack is the amount of time an activity can exceed its early finish date without affecting the early start date of any successor(s). Free slack can never be negative. Only activities that occur at the page 183end of a chain of activities, where you have a merge activity, can have free slack. See Figure 6.8, the Automated Warehouse project.
In Figure 6.8 activity G has free slack of 15 days, while activities B and D do not. In this case, activity G is the last activity in the upper path, and it merges to activity H. Hence, to delay activity G up to 15 days does not delay any following activities and requires no coordination with managers of other activities. Conversely, if either activity B or activity D is delayed, the managers of following activities need to be notified that the slack has been used so they can adjust their start schedules. For example, if activity B is delayed 5 days, the manager of activity B should notify those in charge of the following activities (D and G) that their slack has been reduced to 10 time units and their early start will be delayed 5 days. In this example, activity D cannot then start until day 20, which reduces activity D slack to 10 days (LS − ES = SL or 30 − 20 = 10). Free slack for activity G is also reduced to 10 days.
Free slack occurs at the last activity in a chain of activities. In some situations the “chain” has only one link. Activity F in Figure 6.8 is an example. It has free slack of 35 days. Note that it needs no coordination with other activities—unless a delay exceeds the free slack of 35 days. (Note: The moment you exceed all free slack available, you delay the project and must coordinate with others who are impacted.)
The distinction between free and total slack at first glance seems trivial, but in reality it is very important. When you are responsible for a late activity that has zero free slack, you impact the schedules of subsequent activities. You should notify the managers of the remaining activities in the chain that you will be late. Again, note that total slack is shared across the whole path. Alternatively if you are responsible for an activity that has free slack when you start, you do not need to notify anyone as long as your work does not absorb all of the slack!
6.6 Using the Forward and Backward Pass Information
Returning to the Automated Warehouse project network in Figure 6.8, what does a slack of 35 days for activity F (Develop Patient Request) mean for the project manager? In this specific case it means activity F can be delayed 35 days. In a larger sense the project manager soon learns that free slack is important because it allows flexibility in scheduling scarce project resources—personnel and equipment—that are used on more than one parallel activity or another project.
Knowing the four activity times of ES, LS, EF, and LF is invaluable for the planning, scheduling, and controlling phases of the project. The ES and LF tell the project manager the time interval in which the activity should be completed. For example, activity G (Test Software) must be completed within the time interval 35 and 85 days; the activity can start as early as day 35 or finish as late as day 85. Conversely, activity C (Design Hardware) must start on day 10, or the project will be delayed.
When the critical path is known, it is possible to tightly manage the resources of the activities on the critical path so no mistakes are made that will result in delays. In addition, if for some reason the project must be expedited to meet an earlier date, it is possible to select those activities, or a combination of activities, that will cost the least to shorten the project. Similarly, if the critical path is delayed and the time must be made up by shortening some activity or activities on the critical path to make up any negative slack, it is possible to identify the activities on the critical path that cost the least to shorten. If there are other paths with very little slack, it may be necessary to shorten activities on those paths also.
page 184
6.7 Level of Detail for Activities
Time-phasing work and budgets of the project mandate careful definition of the activities that make up the project network. Typically an activity represents one or more tasks from a work package. How many tasks you include in each activity sets the level of detail. In some cases it is possible to end up with too much information to manage, and this can result in increased overhead costs. Managers of small projects have been able to minimize the level of detail by eliminating some of the preliminary steps to drawing networks. Larger firms also recognize the cost of information overload and are working to cut down the level of detail in networks.
6.8 Practical Considerations
Network Logic Errors
Project network techniques have certain logic rules that must be followed. One rule is that conditional statements such as “if test successful build proto, if failure redesign” are not permitted. The network is not a decision tree; it is a project plan that we assume will materialize. If conditional statements were allowed, the forward and backward pass would make little sense. Although in reality a plan seldom materializes as we expect in every detail, it is a reasonable initial assumption. You will see that once a network plan is developed, it is an easy step to make revisions to accommodate changes.
Another rule that defeats the project network and computation process is looping. Looping is an attempt by the planner to return to an earlier activity. Recall that the activity identification numbers should always be higher for the activities following an activity in question; this rule helps to avoid the illogical precedence relationships among the activities. An activity should only occur once; if it is to occur again, the activity should have a new name and identification number and should be placed in the right sequence on the network. Figure 6.9 shows an illogical loop. If this loop were allowed to exist, this path would perpetually repeat itself. Many computer programs catch this type of logic error.
FIGURE 6.9
Illogical Loop
Activity Numbering
Each activity needs a unique identification code—a letter or a number. In practice very elegant schemes exist. Most schemes number activities in ascending order—that is, each succeeding activity has a larger number so that the flow of the project activities is toward project completion. It is customary to leave gaps between numbers (1, 5, 10, 15, . . .). Gaps are desirable so you can add missing or new activities later. Because it is nearly impossible to draw a project network perfectly, numbering networks is frequently not done until after the network is complete.
In practice you will find computer programs that accept numeric, alphabetic, or a combination of activity designations. Combination designations are often used to identify page 185cost, work skill, department, and location. As a general rule, activity numbering systems should be ascending and as simple as possible. The intent is to make it as easy as you can for project participants to follow work through the network and locate specific activities.
Use of Computers to Develop Networks
All of the tools and techniques discussed in this chapter can be used with the computer software currently available. Two examples are shown in Figures 6.10 and 6.11. Figure 6.10 presents a generic AON computer output for the Automated Warehouse Picking System project. Observe that these computer outputs use numbers to identify activities. The critical path is identified by the nodes (activities) 2, 4, 6, and 9. The activity description is shown on the top line of the activity node. The activity start time and identification are on the second line. The finish time and duration are on the third line of the node. The project starts on January 1 and is planned to finish May 20. Note this sample computer network has included non-workdays of holidays and weekends.
FIGURE 6.10 Automated Warehouse Picking System Network
Figure 6.11 presents an early-start Gantt chart.2 Bar charts are popular because they present an easy-to-understand, clear picture on a time-scaled horizon. They are used during planning, resource scheduling, and status reporting. The format is a two-dimensional representation of the project schedule, with activities down the rows and time across the horizontal axis. In this computer output the shaded bars represent the activity durations. The extended lines from the bars represent slack. For example, “Test Software” (ID # 8) has a duration of 35 days (shaded area of the bar) and 15 days of slack (represented by the extended line). The bar also indicates that Test Software has an early start of February 19 and would finish April 8 but can finish as late as April 29 because it has 15 days of slack. When calendar dates are used on the time axis, Gantt charts provide a clear overview of the project schedule and can often be found posted on the walls of project offices. Unfortunately, when projects have many dependency relationships, the dependency lines soon become overwhelming and defeat the simplicity of the Gantt chart.
Project management software can be a tremendous help in the hands of those who understand and are familiar with the tools and techniques discussed in this text. However, there is nothing more dangerous than someone using the software with little or no knowledge of how the software derives its output. Mistakes in input are very common, and someone skilled in the concepts, tools, and information system is needed to recognize that errors exist so that false actions are avoided.
Calendar Dates
Ultimately you will want to assign calendar dates to your project activities. If a computer program is not used, dates are assigned manually. Lay out a calendar of workdays (exclude non-workdays), and number them. Then relate the calendar workdays to the workdays on your project network. Most computer programs will assign calendar dates automatically after you identify start dates, time units, non-workdays, and other information.
Multiple Starts and Multiple Projects
Some computer programs require a common start and finish event in the form of a node—usually a circle or rectangle—for a project network. Even if this is not a requirement, it is a good idea because it avoids “dangler” paths. Dangler paths give the impression that the project does not have a clear beginning or ending. If a project has more than one activity that can begin when the project is to start, each path is a dangler path. The same is true if a project network ends with more than one activity; these page 186unconnected paths are also called danglers. Danglers can be avoided by tying dangler activities to a common project start or finish node.
page 187
FIGURE 6.11 Automated Warehouse Picking System Gantt Chart
When several projects are tied together in an organization, using a common start and end node helps to identify the total planning period of all projects. Use of pseudo or dummy wait activities from the common start node allows different start dates for each project.
6.9 Extended Network Techniques to Come Closer to Reality
The method for showing relationships among activities in the previous sections is called the finish-to-start relationship because it assumes all immediately preceding connected activities must be completed before the next activity can begin. In an effort to come closer to the realities of projects, some useful extensions have been added. The use of laddering was the first obvious extension practitioners found very useful.
Laddering
The assumption that all immediately preceding activities must be 100 percent complete is too restrictive for some situations found in practice. This restriction occurs most frequently when one activity overlaps the start of another and has a long duration. Under the standard finish-to-start relationship, when an activity has a long duration and will delay the start of an activity immediately following it, the activity can be broken into segments and the network drawn using a laddering approach so the following activity can begin sooner and not delay the work. This segmenting of the larger activity gives the appearance of steps on a ladder on the network, thus the name. The classic example used in many texts and articles is laying pipe, because it is easy to visualize. The trench must be dug, pipe laid, and the trench refilled. If the pipeline is one mile long, it is not necessary to dig one mile of trench before the laying of pipe can begin or to lay one mile of pipe before refill can begin. Figure 6.12 shows how these overlapping activities might appear in an AON network using the standard finish-to-start approach.
FIGURE 6.12
Example of Laddering Using Finish-to-Start Relationship
Use of Lags to Reduce Schedule Detail and Project Duration
The use of lags has been developed to offer greater flexibility in network construction. A lag is the minimum amount of time a dependent activity must be delayed to begin or end. The use of lags in project networks occurs primarily for two reasons:
When activities of long duration delay the start or finish of successor activities, the network designer normally breaks the activity into smaller activities to avoid the page 189long delay of the successor activity. Use of lags can avoid such delays and reduce network detail.
Lags can be used to constrain the start and finish of an activity.
The most commonly used relationship extensions are start-to-start, finish-to-finish, and combinations of these two. These relationship patterns are discussed in this section.
Finish-to-Start Relationship
The finish-to-start relationship represents the typical, generic network style (used in the early part of the chapter). However, there are situations in which the next activity in a sequence must be delayed even when the preceding activity is complete. For example, removing concrete forms cannot begin until the poured cement has cured for two time units. Figure 6.13 shows this lag relationship for AON networks. Finish-to-start lags are frequently used when ordering materials. For example, it may take 1 day to place orders but take 19 days to receive the goods. The use of finish-to-start allows the activity duration to be only 1 day and the lag 19 days. This approach ensures the activity cost is tied to placing the order only, rather than charging the activity for 20 days of work. This same finish-to-start lag relationship is useful to depict transportation, legal, and mail lags.
FIGURE 6.13
Finish-to-Start Relationship
The use of finish-to-start lags should be carefully checked to ensure their validity. Conservative project managers and those responsible for completion of activities have been known to use lags as a means of building in a “slush” factor to reduce the risk of being late. A simple rule to follow is that the use of finish-to-start lags must be justified and approved by someone responsible for a large section of the project. The legitimacy of lags is not usually difficult to discern. The legitimate use of the additional relationship shown can greatly enhance the network by more closely representing the realities of the project.
Start-to-Start Relationship
An alternative to segmenting the activities, as we did earlier, is to use a start-to-start relationship. Typical start-to-start relationships are shown in Figure 6.14. Figure 6.14A page 190shows the start-to-start relationship with zero lag in which on a movie set you would want filming and recording audio to start simultaneously. Figure 6.14B shows the same relationship with a lag of five time units. It is important to note that the relationship may be used with or without a lag. If time is assigned, it is usually shown on the dependency arrow of an AON network.
FIGURE 6.14
Start-to-Start Relationship
In Figure 6.14B, testing cannot begin until five time units after coding begins. This type of relationship typically depicts a situation in which you can perform a portion of one activity and begin a following activity before completing the first. This relationship can be used on the pipe-laying project. Figure 6.15 shows the project using an AON network. The start-to-start relationship reduces network detail and project delays by using lag relationships.
FIGURE 6.15
Use of Lags to Reduce Project Duration
It is possible to find compression opportunities by changing finish-to-start relationships to start-to-start relationships. A review of finish-to-start critical activities may point out opportunities that can be revised to be parallel by using start-to-start relationships. For example, in place of a finish-to-start activity “design house, then build foundation,” a start-to-start relationship could be used in which the foundation can be started, say, five days (lag) after design has started—assuming the design of the foundation is the first part of the total design activity. This start-to-start relationship with a small lag allows a sequential activity to be worked on in parallel and to compress the duration of the critical path. This same concept is frequently found in projects in which concurrent engineering is used to speed completion of a project. Concurrent engineering, which is highlighted in Snapshot from Practice 6.3: Concurrent Engineering, basically breaks activities into smaller segments so that work can be done in parallel and the project expedited (Turtle, 1994). Start-to-start relationships can depict the concurrent engineering conditions and reduce network detail. Of course, the same result can be accomplished by breaking an activity into small packages that can be implemented in parallel, but this latter approach increases the network and tracking detail significantly.
page 191
page 192
Finish-to-Finish Relationship
This relationship is shown in Figure 6.17. The finish of one activity depends on the finish of another activity. For example, testing cannot be completed any earlier than four days after the prototype is complete. Note that this is not a finish-to-start relationship because the testing of subcomponents can begin before the prototype is completed, but four days of “system” testing is required after the prototype is finished.
FIGURE 6.17
Finish-to-Finish Relationship
Start-to-Finish Relationship
This relationship represents situations in which the finish of an activity depends on the start of another activity. For example, system documentation cannot end until three days after testing has started (see Figure 6.18). All the relevant information to complete the system documentation is produced after the first three days of testing.
FIGURE 6.18
Start-to-Finish Relationship
Combinations of Lag Relationships
More than one lag relationship can be attached to an activity. These relationships are usually start-to-start and finish-to-finish combinations tied to two activities. For example, debug cannot begin until two time units after coding has started. Coding must be finished four days before debug can be finished (see Figure 6.19).
FIGURE 6.19
Combination Relationships
An Example Using Lag Relationships—the Forward and Backward Pass
The forward and backward pass procedures are the same as explained earlier in the chapter for finish-to-start relationships (without lags). The modifying technique lies in the need to check each new relationship to see if it alters the start or finish time of another activity.
An example of the outcome of the forward and backward pass is shown in Figure 6.20. Order hardware depends upon the design of the system (start-to-start). Three days into the design of the system (activity A), it is possible to order the required hardware (activity B). It takes four days after the order is placed (activity B) for the hardware to arrive so it can begin to be installed (activity C). After two days of installing the software system (activity D), the testing of the system can begin (activity E). System testing (activity E) can be completed one day after the software is installed (activity D). Preparing system documentation (activity F) can begin once the design is completed (activity A), but it cannot be completed until two days after testing the system (activity E) is completed. This final relationship is an example of a finish-to-finish lag.
Note how an activity can have a critical finish and/or start. Activities E and F have critical finishes (zero slack), but their activity starts have 3 and 11 days of slack. It is page 193only the finishes of activities E and F that are critical. Conversely, activity A has zero slack to start but has five days of slack to finish. So, for example, the project team realize they have some flexibility in scheduling a portion of the testing work (activity E) up until the installation of software (activity D), at which time they know to be ready to complete the testing within one day after the installation.
The critical path follows activity start and finish constraints that occur due to the use of the additional relationships available and the imposed lags. You can identify the critical path in Figure 6.20 by following the dashed line on the network.
FIGURE 6.20 Network Using Lags
If a lag relationship exists, each activity must be checked to see if the start or finish is constrained. For example, in the forward pass the EF of activity E (test system) (17) is controlled by the finish of activity D (install software) and the lag of one time unit (16 + lag 1 = 17). Finally, in the backward pass the LS of activity A (design system) is controlled by activity B (order hardware) and the lag relationship to activity A (3 − 3 = 0).
Hammock Activities
Another of the extended techniques uses a hammock activity. This type of activity derives its name because it spans over a segment of a project. The hammock activity duration is determined after the network plan is drawn. Hammock activities are frequently used to identify the use of fixed resources or costs over a segment of the project. Typical examples of hammock activities are inspection services, consultants, and construction management services.
A hammock activity derives its duration from the time span between other activities. For example, a special color copy machine is needed for a segment of a tradeshow publication project. A hammock activity can be used to indicate the need for this resource and to apply costs over this segment of the project. This hammock is linked page 194from the start of the first activity in the segment that uses the color copy machine to the end of the last activity that uses it. The hammock duration is simply the difference between the EF for the last activity and the ES of the first activity. The duration is computed after the forward pass and hence has no influence on other activity times. Figure 6.21 provides an example of a hammock activity used in a network. The duration for the hammock activity is derived from the early start of activity B and the early finish of activity F—that is, the difference between 13 and 5, or 8 time units. The hammock duration will change if any ES or EF in the chain-sequence changes. Hammock activities are very useful in assigning and controlling indirect project costs.3
FIGURE 6.21 Hammock Activity Example
Another major use of hammock activities is to aggregate sections of a project. This is similar to developing a subnetwork, but the precedence is still preserved. This approach is sometimes used to present a “macro network” for upper management levels. Using a hammock activity to group activities can facilitate getting the right level of detail for specific sections of a project.
Summary
Many project managers feel the project network is their most valuable exercise and planning document. Project networks sequence and time-phase the project work, resources, and budgets. Work package tasks are used to develop activities for networks.
Every project manager should feel comfortable working in an AON environment. The AON method uses nodes (boxes) for activities and arrows for dependencies. The forward and backward pass establishes early and late times for activities as well as slack. The critical path is the longest activity path(s) through the network. Any delay page 195in an activity on the critical path will delay the project completion, assuming everything else goes according to plan. On time-sensitive projects, project managers monitor the critical path closely, often assigning their best personnel to those activities.
Several extensions and modifications have been appended to the original AON method. Lags allow the project planner to more closely replicate the conditions found in practice. The use of lags can result in the start or finish of an activity becoming critical. Some computer software simply calls the whole activity critical rather than identifying the start or finish as being critical. Caution should be taken to ensure that lags are not used as a buffer for possible errors in estimating time. Finally, hammock activities are useful in tracking the costs of resources used for a particular segment of a project. Hammock activities can also be used to reduce the size of a project network by grouping activities for simplification and clarity. All of the discussed refinements to the original AON methodology contribute toward better planning and control of projects.
Key Terms
Review Questions
How does the WBS differ from the project network?
How are WBS and project networks linked?
Why bother creating a WBS? Why not go straight to a project network and forget the WBS?
Why is slack important to the project manager?
What is the difference between free slack and total slack?
Why are lags used in developing project networks?
What is a hammock activity and when is it used?
SNAPSHOT 
FROM PRACTICE
Discussion Questions
6.2 The Critical Path
Why is it important to identify the critical path before starting a project?
On what kind of projects would the critical path be irrelevant?
6.3 Concurrent Engineering (Fast Tracking)
What are the disadvantages of concurrent engineering (fast tracking)?
What kinds of projects should avoid using concurrent engineering?
Exercises
Creating a Project Network
Here is a partial work breakdown structure for a wedding. Use the method described in Snapshot from Practice 6.1: The Yellow Sticky Approach to create a network for this project.
page 196
Note: Do not include summary tasks in the network (i.e., 1.3, Ceremony, is a summary task; 1.2, Marriage license, is not a summary task). Do not consider who would be doing the task in building the network. For example, do not arrange “hiring a band” to occur after “florist” because the same person is responsible for doing both tasks. Focus only on technical dependencies between tasks.
Hint: Start with the last activity (wedding reception), and work your way back to the start of the project. Build the logical sequence of tasks by asking the following question: in order to have or do this, what must be accomplished immediately before this? Once completed, check forward in time by asking this question: is this task the only thing that is needed immediately before the start of the next task?
Work Breakdown Structure
Wedding project
1.1 Decide on date
1.2 Marriage license
1.3 Ceremony
1.3.1 Rent church
1.3.2 Florist
1.3.3 Create/print programs
1.3.4 Hire photographer
1.3.5 Wedding ceremony
1.4 Guests
1.4.1 Develop guest list
1.4.2 Order invitations
1.4.3 Address and mail invitations
1.4.4 Track RSVPs
1.5 Reception
1.5.1 Reserve reception hall
1.5.2 Food and beverage
1.5.2.1 Choose caterer
1.5.2.2 Decide on menu
1.5.2.3 Make final order
1.5.3 Hire DJ
1.5.4 Decorate reception hall
1.5.5 Wedding reception
Drawing AON Networks
Draw a project network from the following information. What activity(ies) is a burst activity? What activity(ies) is a merge activity?
ID Description Predecessor A Survey site None B Excavate site A C Install power lines B D Install drainage B E Pour foundation C, D page 197Draw a project network from the following information.* What activity(ies) is a burst activity? What activity(ies) is a merge activity?
ID Description Predecessor A Identify topic None B Research topic A C Draft paper B D Edit paper C E Create graphics C F References C G Proof paper D, E, F H Submit paper G Draw a project network from the following information. What activity(ies) is a burst activity? What activity(ies) is a merge activity?
ID Description Predecessor A Contract signed None B Survey designed A C Target market identified A D Data collection B, C E Develop presentation B F Analyze results D G Demographics C H Presentation E, F, G Draw a project network from the following information. What activity(ies) is a burst activity? What activity(ies) is a merge activity?
ID Description Predecessor A Order review None B Order standard parts A C Produce standard parts A D Design custom parts A E Software development A F Manufacture custom parts C, D G Assemble B, F H Test E, G
AON Network Times
From the following information, develop an AON project network. Complete the forward and backward pass, compute activity slack, and identify the critical path. How many days will the project take?
ID Description Predecessor Time A Survey site None 2 B Excavate site A 4 C Install power lines B 3 D Install drainage B 5 E Pour foundation C, D 3 page 198The project information for the custom order project of the Air Control Company is presented here. Draw a project network for this project. Compute the early and late activity times and slack times. Identify the critical path.
ID Description Predecessor Time A Order review None 2 B Order standard parts A 3 C Produce standard parts A 10 D Design custom parts A 13 E Software development A 18 F Manufacture custom hardware C, D 15 G Assemble B, F 10 H Test E, G 5 You have signed a contract to build a garage for the Simpsons. You will receive a $500 bonus for completing the project within 17 working days. The contract also contains a penalty clause in which you will lose $100 for each day the project takes longer than 17 working days.
Draw a project network, given the following information. Complete the forward and backward pass, compute activity slack, and identify the critical path. Do you expect to receive a bonus or a penalty on this project?
ID Description Predecessor Time (days) A Prepare site None 2 B Pour foundation A 3 C Erect frame B 4 D Roof C 4 E Windows C 1 F Doors C 1 G Electrical C 3 H Rough-in-frame D, E, F, G 2 I Door opener F, G 1 J Paint H, I 2 K Cleanup J 1 You are creating a customer database for the Hillsboro Hops minor league baseball team. Draw a project network, given the information in the table that follows. Complete the forward and backward pass, compute activity slack, and identify the critical path.
How long will this project take? How sensitive is the network schedule? Calculate the free slack and total slack for all noncritical activities.
ID Description Predecessor Time (days) A Systems design None 2 B Subsystem A design A 1 C Subsystem B design A 1 D Subsystem C design A 1 E Program A B 2 F Program B C 2 G Program C D 2 H Subsystem A test E 1 I Subsystem B test F 1 J Subsystem C test G 1 K Integration H, I, J 3 L Integration test K 1 page 199 K. Nelson, project manager of Print Software, Inc., wants you to prepare a project network; compute the early, late, and slack activity times; determine the planned project duration; and identify the critical path. His assistant has collected the following information for the color printer drivers software project:
ID Description Predecessor Time A External specifications None 8 B Review design features A 2 C Document new features A 3 D Write software A 60 E Program and test B 40 F Edit and publish notes C 2 G Review manual D 2 H Alpha site E, F 20 I Print manual G 10 J Beta site H, I 10 K Manufacture J 12 L Release and ship K 3 A large Southeast city is requesting federal funding for a park-and-ride project.* One of the requirements in the request application is a network plan for the design phase of the project. Sophie Kim, the chief engineer, wants you to develop a project network plan to meet this requirement. She has gathered the activity time estimates and their dependencies shown here. Show your project network with the activity early, late, and slack times. Mark the critical path.
ID Description Predecessor Time A Survey None 5 B Soils report A 20 C Traffic design A 30 D Lot layout A 5 E Approve design B, C, D 80 F Illumination E 15 G Drainage E 30 H Landscape E 25 I Signage E 15 J Bid proposal F, G, H, I 10 You are creating a customer database for the Lehigh Valley IronPigs minor league baseball team. Draw a project network, given the following information. Complete the forward and backward pass, compute activity slack, and identify the critical path.
How long will this project take? How sensitive is the network schedule? Calculate the free slack and total slack for all noncritical activities.
ID Description Predecessor Time (days) A Systems design None 2 B Subsystem A design A 1 C Subsystem B design A 2 D Subsystem C design A 1 E Program A B 2 F Program B C 10 G Program C D 3 H Subsystem A test E 1 I Subsystem B test F 1 J Subsystem C test G 1 K Integration H, I, J 3 L Integration test K 1 page 200You are completing a group term paper.* Given the project network that follows, complete the forward and backward pass, compute activity slack, and identify the critical path. Use this information to create a Gantt chart for the project. Be sure to show slack for noncritical activities.
You are managing a product upgrade project for Bangkokagogo. Given the project network that follows, complete the forward and backward pass, compute activity slack, and identify the critical path. Use this information to create a Gantt chart for the project. Be sure to show slack for noncritical activities.
page 201
Product Upgrade Project Gantt Chart
You are creating a database for the Oklahoma City Thunder NBA basketball team. Given the project network that follows, complete the forward and backward pass, compute activity slack, and identify the critical path. Use this information to create a Gantt chart for the project.
page 202
Computer Exercises
The Planning Department of an electronics firm has set up the activities for development and production of a new MP3 player. Given the following information, develop a project network using Microsoft Project. Assume a five-day workweek and the project starts on January 4, 2017.
Activity ID Description Activity Predecessor Activity Time (weeks) 1 Staff None 2 2 Develop market program 1 3 3 Select channels of distribution 1 8 4 Patent 1 12 5 Pilot production 1 4 6 Test market 5 4 7 Ad promotion 2 4 8 Set up for production 4, 6 16 The project team has requested that you create a network for the project and determine if the project can be completed in 45 weeks.
Using Microsoft Project, set up the network and determine the critical path for phase 1 of the Whistler Ski Resort project. The project workweek will be five days (M–F).
Whistler Ski Resort Project
Given the fact that the number of skiing visitors to Whistler, B.C., Canada, has been increasing at an exciting rate, thanks to the 2010 Winter Olympics, the Whistler Ski Association has been considering construction of another ski lodge and ski complex. The results of an economic feasibility study just completed by members of the staff show that a winter resort complex near the base of Whistler Mountain could be a very profitable venture. The area is accessible by car, bus, train, and air. The board of directors has voted to build the 10-million-dollar complex recommended in the study. Unfortunately, due to the short summer season, the complex will have to be built in stages. The first stage (year 1) will contain a day lodge, chair lift, rope tow, generator house (for electricity), and parking lot designed to accommodate 400 cars and 30 buses. The second and third stages will include a hotel, an ice rink, a pool, shops, two additional chair lifts, and other attractions. The board has decided that stage one should begin no later than April 1 and be completed by October 1, in time for the next skiing season. You have been assigned the task of project manager, and it is your job to coordinate the ordering of materials and construction activities to ensure the project’s completion by the required date.
After looking into the possible sources of materials, you are confronted with the following time estimates. Materials for the chair lift and rope tow will take 30 days and 12 days, respectively, to arrive once the order is submitted. Lumber for the day lodge, generator hut, and foundations will take 9 days to arrive. The electrical and plumbing materials for the day lodge will take 12 days to arrive. The generator will take 12 days to arrive. Before actual construction can begin on the various facilities, a road to the site must be built; this will take 6 days. As soon as the road is in, clearing can begin concurrently on the sites of the day lodge, generator house, chair lift, and rope tow. It is estimated that the clearing task at each site will take 6 days, 3 days, 36 days, and 6 days, respectively. The clearing of the main ski slopes can begin after the area for the chair lift has been cleared; this will take 84 days.
The foundation for the day lodge will take 12 days to complete. Construction of the main framework will take an additional 18 days. After the framework is completed, electrical wiring and plumbing can be installed concurrently. These should take 24 and page 20330 days, respectively. Finally, the finishing construction on the day lodge can begin; this will take 36 days.
Installation of the chair lift towers (67 days) can begin once the site is cleared, lumber delivered, and foundation completed (6 days). Also, when the chair lift site has been cleared, construction of a permanent road to the upper towers can be started; this will take 24 days. While the towers are being installed, the electric motor to drive the chair lift can be installed; the motor can be installed in 24 days. Once the towers are completed and the motor installed, it will take 3 days to install the cable and an additional 12 days to install the chairs.
Installation of the towers for the rope tow can begin once the site is cleared and the foundation is built and poured; it takes 4 days to build the foundation, pour the concrete, and let it cure and 20 days to install the towers for the rope tow. While the towers are being erected, installation of the electric motor to drive the rope tow can begin; this activity will take 24 days. After the towers and motor are installed, the rope tow can be strung in 1 day. The parking lot can be cleared once the rope tow is finished; this task will take 18 days.
The foundation for the generator house can begin at the same time as the foundation for the lodge; this will take 6 days. The main framework for the generator house can begin once the foundation is completed; framing will take 12 days. After the house is framed, the diesel generator can be installed in 18 days. Finishing construction on the generator house can now begin and will take 12 more days.
Assignment
Identify the critical path on your network.
Can the project be completed by October 1?
Optical Disk Preinstallation Project
The optical disk project team has started gathering the information necessary to develop the project network—predecessor activities and activity times in weeks. The results of their meeting are found in the following table.
Activity Description Duration Predecessor 1 Define scope 6 None 2 Define customer problems 3 1 3 Define data records and relationships 5 1 4 Mass storage requirements 5 2, 3 5 Consultant needs analysis 10 2, 3 6 Prepare installation network 3 4, 5 7 Estimate costs and budget 2 4, 5 8 Design section “point” system 1 4, 5 9 Write request proposal 5 4, 5 10 Compile vendor list 3 4, 5 11 Prepare mgmt. control system 5 6, 7 12 Prepare comparison report 5 9, 10 13 Compare system “philosophies” 3 8, 12 14 Compare total installation 2 8, 12 15 Compare cost of support 3 8, 12 16 Compare customer satisfaction level 10 8, 12 17 Assign philosophies points 1 13 18 Assign installation cost 1 14 19 Assign support cost 1 15 20 Assign customer satisfaction points 1 16 21 Select best system 1 11, 17, 18, 19, 20 22 Order system 1 21
The project team has requested that you create a network for the project and determine if the project can be completed in 45 weeks.
page 204
Lag Exercises
From the following information, compute the early, late, and slack times for each activity. Identify the critical path.
Given the following information, compute the early, late, and slack times for the project network. Which activities on the critical path have only the start or finish of the activity on the critical path?
page 205Given the information in the following lag exercises, compute the early, late, and slack times for the project network.* Which activities on the critical path have only the start or finish of the activity on the critical path?
Given the following network, compute the early, late, and slack time for each activity. Clearly identify the critical path.
page 206
CyClon Project
The CyClon project team has started gathering the information necessary to develop a project network—predecessor activities and activity time in days. The results of their meeting are found in the following table.
Activity Description Duration Predecessor 1 CyClon Project 2 Design 10 3 Procure prototype parts 10 2 4 Fabricate parts 8 2 5 Assemble prototype 4 3, 4 6 Laboratory test 7 5 7 Field test 10 6 8 Adjust design 6 7 9 Order stock components 10 8 10 Order custom components 15 8 11 Assemble test production unit 10 9, 10 12 Test unit 5 11 13 Document results 3 12
Part A. Create a network based on the information in the table. How long will the project take? What is the critical path?
Part B. Upon further review the team recognize that they missed three finish-to-start lags. Procure prototype parts will involve only 2 days of work but it will take 8 days for the parts to be delivered. Likewise, Order stock components will take 2 days of work and 8 days for delivery and Order custom components will take 2 days of work and 13 days for delivery.
Reconfigure the CyClon schedule by entering the three finish-to-start lags. What impact did these lags have on the original schedule? On the amount of work required to complete the project?
Part C. Management is still not happy with the schedule and wants the project completed as soon as possible. Unfortunately, they are not willing to approve additional resources. One team member pointed out that the network contained only finish-to-start relationships and that it might be possible to reduce project duration by creating start-to-start lags. After much deliberation the team concluded that the following relationships could be converted into start-to-start lags:
Procure prototype parts could start 6 days after the start of Design.
Fabricate parts could start 9 days after the start of Design.
Laboratory test could begin 1 day after the start of Assemble prototype.
Field test could start 5 days after the start of Laboratory test.
Adjust design could begin 7 days after the start of Field test.
Order stock and Order custom components could begin 5 days after Adjust design.
Test unit could begin 9 days after the start of Assemble test production unit.
Document results could start 3 days after the start of Test unit.
Reconfigure the CyClon schedule by entering all nine start-to-start lags. What impact did these lags have on the original schedule (Part A)? How long will the project take? Is there a change in the critical path? Is there a change in the sensitivity of the network? Why would management like this solution?
*The solution to this exercise can be found in Appendix One.
*The solution to this exercise can be found in Appendix One.
*The solution to this exercise can be found in Appendix One.
*The solution to this exercise can be found in Appendix One.
page 207
References
Gantt, H. L., Work, Wages and Profit, published by The Engineering Magazine, New York, 1910; republished as Work, Wages and Profits (Easton, PA: Hive, 1974).
Gray, C. F., Essentials of Project Management (Princeton, NJ: PBI, 1981).
Kelly, J. E., “Critical Path Planning and Scheduling: Mathematical Basis,” Operations Research, vol. 9, no. 3 (May/June 1961), pp. 296–321.
Levy, F. K., G. L. Thompson, and J. D. West, “The ABCs of the Critical Path Method,” Harvard Business Review, vol. 41, no. 5 (1963), pp. 98–108.
Rosenblatt, A., and G. Watson, “Concurrent Engineering,” IEEE Spectrum, July 1991, pp. 22–37.
Turtle, Q. C., Implementing Concurrent Project Management (Englewood Cliffs, NJ: Prentice Hall, 1994).
Case 6.1
Advantage Energy Technology Data Center Migration*—Part A
Brian Smith, network administrator at Advanced Energy Technology (AET), has been given the responsibility of implementing the migration of a large data center to a new office location. Careful planning is needed because AET operates in the highly competitive petroleum industry. AET is one of five national software companies that provide an accounting and business management package for oil jobbers and gasoline distributors. A few years ago AET jumped into the “application service provider” world. Their large data center provides clients with remote access to AET’s complete suite of application software systems. Traditionally, one of AET’s primary competitive advantages has been the company’s trademark IT reliability. Due to the complexity of this project, Brian will have to use a parallel method of implementation. Although this will increase project costs, a parallel approach is essential if reliability is not to be compromised.
Currently AET’s data center is located on the second floor of a renovated old bank building in downtown Corvallis, Oregon. The company is moving to a new, one-level building in the recently developed industrial complex at the Corvallis International Airport. On February 1, Brian is formally assigned the task by the vice president of operations, Dan Whitmore, with the following guidelines:
From start to finish, it is anticipated the entire project will take three to four months to complete.
It is essential that AET’s 235 clients suffer no downtime.
Whitmore advises Brian to come back to the Executive Committee on February 15 with a presentation on the scope of the project that includes costs, “first-cut” timeline, and proposed project team members.
Brian had some preliminary discussions with some of AET’s managers and directors from each of the functional departments and then arranged for a full-day scope page 208meeting on February 4 with a few of the managers and technical representatives from Operations, Systems, Facilities, and Applications. The scope team determined the following:
Three to four months is a feasible project timeline, and first-cut cost estimate is $80,000–$90,000 (this includes the infrastructure upgrade of the new site).
Critical to the “no-downtime” requirement is the need to completely rely on AET’s remote disaster recovery “hot” site for full functionality.
Brian will serve as project manager of a team consisting of one team member each from Facilities, Operations/Systems, Operations/Telecommunications, Systems and Applications, and Customer Service.
Brian’s Executive Committee report was positively received and, after a few modifications and recommendations, he was formally charged with responsibility for the project. Brian recruited his team and scheduled their first team meeting (March 1) as the initial task of his project-planning process.
Once the initial meeting is conducted Brian can hire the contractors to renovate the new data center. During this time Brian will figure out how to design the network. Brian estimates that screening and hiring a contractor will take about one week and that the network design will take about two weeks. The new center requires a new ventilation system. The manufacturer’s requirements include an ambient temperature of 67 degrees to keep all of the data servers running at optimal speeds. The ventilation system has a lead time of three weeks. Brian will also need to order new racks to hold the servers, switches, and other network devices. The racks have a two-week delivery time.
The data center supervisor requested that Brian replace all of the old power supplies and data cables. Brian will need to order these as well. Because Brian has a great relationship with the vendor, they guarantee that it will take only one week lead time for the power supplies and the data cables. Once the new ventilation system and racks arrive, Brian can begin installing them. It will take one week to install the ventilation system and three weeks to install the racks. The renovation of the new data center can begin as soon as the contractors have been hired. The contractors tell Brian that construction will take 20 days. Once the construction begins and after Brian installs the ventilation system and racks, the city inspector must approve the construction of the raised floor.
The city inspector will take two days to approve the infrastructure. After the city inspection and after the new power supplies and cables have arrived, Brian can install the power supplies and run the cables. Brian estimates that it will take five days to install the power supplies and one week to run all of the data cables. Before Brian can assign an actual date for taking the network off line and switching to the hot remote site, he must get approval from each of the functional units (“switchover approval”). Meetings with each of the functional units will require one week. During this time he can initiate a power check to ensure that each of the racks has sufficient voltage. This will require only one day.
Upon completion of the power check, he can take one week to install his test servers. The test servers will test all of the primary network functions and act as a safeguard before the network is taken off line. The batteries must be charged, ventilation installed, and test servers up and running before management can be assured that the new infrastructure is safe, which will take two days. Then they will sign off the primary systems check, taking one day of intense meetings. They will also set an official date for the network move.
page 209
Brian is happy that everything has gone well thus far and is convinced that the move will go just as smoothly. Now that an official date is set, the network will be shut down for a day. Brian must move all of the network components to the new data center. Brian will do the move over the weekend—two days—when user traffic is at a low point.
ASSIGNMENT
Generate a priority matrix for AET’s system move.
Develop a WBS for Brian’s project. Include duration (days) and predecessors.
Using a project-planning tool, generate a network diagram for this project.
Note: Base your plan on the following guidelines: eight-hour days, five-day weeks except for when Brian moves the network components over a weekend, no holiday breaks, and March 1, 2010, is the project start date. Ordering ventilation system, new racks, and power supplies/cables takes only one actual day of work. The remaining days are the time necessary for the vendors to fill and ship the order to Brian. So use finish-to-start lags here. Assume that five days after the start of the renovation of the data center that the raised floor will be ready for inspection (a start-to-start lag).
*Prepared by James Moran, a project management instructor at the College of Business, Oregon State University.
Case 6.2
Ventura Baseball Stadium—Part A
The G&E Company is preparing a bid to build the new 47,000-seat Shoreline baseball stadium. The construction must start on June 10, 2019, and be completed in time for the start of the 2022 season. A penalty clause of $500,000 per day of delay beyond April 3rd is written into the contract.
Percival Young, the president of the company, expressed optimism at obtaining the contract and revealed that the company could net as much as $5 million on the project. He also said that if they were successful, the prospects of future projects would be bright, since there is a projected renaissance in building classic ball parks with modern luxury boxes.
ASSIGNMENT
Given the information provided in Table 6.3, construct a network schedule for the stadium project and answer the following questions:
Can the project be completed by the April 3rd deadline? How long will it take?
What is the critical path for the project?
Based on the schedule, would you recommend that G&E pursue this contact? Why? Include a one-page Gantt chart for the stadium schedule.
TABLE 6.3 Ventura Baseball Stadium Case
| ID | Activity | Duration | Predecessor(s) |
| 1 | Baseball Stadium | ||
| 2 | Clear stadium site | 60 days | — |
| 3 | Demolish building | 30 days | 2 |
| 4 | Set up construction site | 30 days | 2 |
| 5 | Drive support piling | 120 days | 2 |
| 6 | Pour lower concrete bowl | 120 days | 5 |
| 7 | Pour main concourse | 120 days | 4, 6 |
| 8 | Install playing field | 90 days | 4, 6 |
| 9 | Construct upper steel bowl | 120 days | 4, 6 |
| 10 | Install seats | 140 days | 7, 9 |
| 11 | Build luxury boxes | 90 days | 7, 9 |
| 12 | Install jumbotron | 30 days | 7, 9 |
| 13 | Stadium infrastructure | 120 days | 7, 9 |
| 14 | Construct steel canopy | 75 days | 10 |
| 15 | Light installation | 30 days | 14 |
| 16 | Build roof supports | 90 days | 6 |
| 17 | Construct roof | 180 days | 16 |
| 18 | Install roof tracks | 90 days | 16 |
| 19 | Install roof | 90 days | 17, 18 |
| 20 | Inspection | 20 days | 8, 11, 13, 15, 19 |
page 210
Case Appendix
Technical Details for the Ventura Baseball Stadium
The baseball stadium is an outdoor structure with a retractable roof. The project begins with clearing the site, an activity that lasts 60 days. Once the site is clear, work can start simultaneously on the structure itself and demolition of an adjacent building site. This demolition is necessary to create a construction stage for storing materials and equipment. It will take 30 days to demolish the buildings and another 30 days to set up the construction site.
The work on the stadium begins by driving 160 support pilings, which will take 120 days. Next comes the pouring of the lower concrete bowl (120 days). Once this is done and the construction site has been set up, then the pouring of the main concourse (120 days), installation of the playing field (90 days), and construction of the upper steel bowl can occur (120 days).
Once the concourse and upper bowl are completed, work can start simultaneously on building the luxury boxes (90 days), installing the seats (140 days), installing the Jumbotron (30 days), and installing the stadium infrastructure (120 days), which includes bathrooms, lockers, restaurants, etc. Once the seats are installed, then the steel canopy can be constructed (75 days), followed by installation of the lights (30 days). The retractable roof represents the most significant technical challenge to the project. page 211Building the roof track supports (90 days) can begin after the lower concrete bowl is constructed. At this time the dimensions of the roof can be finalized and the construction of the roof at a separate site can begin (180 days). After the roof supports are completed, then the roof tracks can be installed (90 days). Once the tracks and roof are completed, then the roof can be installed and made operational (90 days). Once all activities are completed, it will take 20 days to inspect the stadium.
For purposes of this case assume the following:
The following holidays are observed: January 1, Martin Luther King Day (third Monday in January), Memorial Day (last Monday in May), July 4th, Labor Day (first Monday in September), Thanksgiving Day (fourth Thursday in November), December 25 and 26.
If a holiday falls on a Saturday, Friday will be given as an extra day off, and if it falls on a Sunday, Monday will be given as a day off.
The construction crew works Monday through Friday.
Design elements: Snapshot from Practice, Highlight box, Case icon: ©Sky Designs/Shutterstock
1 This process could be clarified and improved by using a simple responsibility matrix (see Chapter 4).
2 Gantt charts were introduced over 100 years ago by Henry Gantt.
3 In order to designate G as a hammock activity in MS Project 2012, you would copy and paste for activity G the start date of activity B and the finish date for activity F (http://support.microsoft.com/kb/141733).