Constructing a Gantt Chart and Network Diagram at Pine Valley Furniture-Representing and Scheduling Project Plans
Constructing a Gantt Chart and Network Diagram at Pine Valley Furniture.
Although Pine Valley Furniture has historically been a manufacturing company, it recently entered the direct sales market for selected target markets.One of the fastest growing of these markets is economically priced furniture suitable for college students. Management has requested that a new Sales Promotion Tracking System (SPTS) be developed. This project has already successfully moved through project initiation and is currently in the detailed project planning stage, which corresponds to the SDLC phase of project initiation and planning. The SPTS will be used to track the sales purchases by college students for the next fall semester. Students typically purchase low-priced beds, bookcases, desks, tables, chairs, and dressers. Because PVF does not normally stock a large quantity of lower-priced items, management feels that a tracking system will help provide information about the college student market that can be used for follow-up sales promotions (e.g., a midterm futon sale).
The project is to design, develop, and implement this information system before the start of the fall term in order to collect sales data at the next major buying period. This deadline gives the project team twenty-four weeks to develop and implement the system. The Systems Priority Board at PVF wants to make a decision this week based on the feasibility of completing the project within the twenty-four-week deadline. Using PVF’s project planning methodology, the project manager, Jim Woo, knows that the next step is to construct a Gantt chart and a Network diagram of the project to represent the baseline project plan so that he can use these charts to estimate the likelihood of completing the project within twenty-four weeks. A major activity of project planning focuses on dividing the project into manageable activities, estimating times for each, and sequencing their order. Here are the steps Jim followed:
1. Identify each activity to be completed in the project. After discussing the new Sales Promotion Tracking System with PVF’s management, sales, and development staff, Jim identified the following major activities for the project:
- Requirements collection
- Screen design
- Report design
- Database design
- User documentation creation
- Software programming
- System testing
- System installation
2. Determine time estimates and calculate the expected completion time for each activity. After identifying the major project activities, Jim established optimistic, realistic, and pessimistic time estimates for each activity. These numbers were then used to calculate the expected completion times for all project activities. Figure 3-23 shows the estimated time calculations for each activity of the Sales Promotion Tracking System project.
3. Determine the sequence of the activities and precedence relationships among all activities by constructing a Gantt chart and Network diagram. This step helps you understand how various activities are related. Jim starts by determining the order in which activities should take place. The results of this analysis for the SPTS project are shown in Figure 3-24. The first row of this figure shows that no activities precede requirements collection. Row 2 shows that screen design must be preceded by requirements collection. Row 4 shows that both screen
FIGURE 3-23 Expected time calculations for the SPTS project.
FIGURE 3-24 Sequence of activities within the SPTS project.
and report design must precede database design. Thus, activities may be preceded by zero, one, or more activities. Using the estimated times and activity sequencing information from Figures 3-23 and 3-24, Jim can now construct a Gantt chart and Network diagram of the project’s activities. To construct the Gantt chart, a horizontal bar is drawn for each activity that reflects its sequence and duration, as shown in Figure 3-25. The Gantt chart may not, however, show direct interrelationships between activities. For example, just because the database design activity begins right after the screen design and report design bars finish does not imply that
FIGURE 3-25 Gantt chart that illustrates the sequence and duration of each activity of the SPTS project.
FIGURE 3-26 A Network diagram that illustrates the activities (circles) and the sequence (arrows) of those activities.
these two activities must finish before database design can begin. To show such precedence relationships, a Network diagram must be used. The Gantt chart in Figure 3-25 does, however, show precedence relationships.
Network diagrams have two major components: arrows and nodes. Arrows reflect the sequence of activities, whereas nodes reflect activities that consume time and resources. A Network diagram for the SPTS project is shown in Figure 3-26. This diagram has eight nodes labeled 1 through 8.
4. Determine the critical path. The critical path of a Network diagram is represented by the sequence of connected activities that produces the shortest overall time period. All nodes and activities within this sequence are referred to as being “on” the critical path. The critical path represents the shortest time in which a project can be completed. In other words, any activity on the critical path that is delayed in completion delays the entire project. Nodes not on the critical path, however, can be delayed (for some amount of time) without delaying the final completion of the project. Nodes not on the critical path contain slack time and allow the project manager some flexibility in scheduling.
Figure 3-27 shows the Network diagram that Jim constructed to determine the critical path and expected completion time for the SPTS project. To determine the critical path, Jim calculated the earliest and latest expected completion time for each activity. He found each activity’s earliest expected completion time (TE) by summing the expected completion times (ET) of the activity and each preceding activity from left to right (i.e., in precedence order), starting at activity 1 and working toward activity 8. In this case, TE for activity 8 is equal to 22 weeks. If two or more activities precede an activity, the largest expected completion time of these activities is used in calculating the new activity’s expected
FIGURE 3-27 A Network diagram for the SPTS project showing estimated times for each activity and the earliest and latest expected completion time for each activity.
FIGURE 3-28 Activity slack time calculations for the SPTS project all activities except number 5 are on the critical path.
completion time. For example, because activity 8 is preceded by both activities 5 and 7, the largest expected completion time between 5 and 7 is 21, so TE for activity 8 is 21 1, or 22. The earliest expected completion time for the last activity of the project represents the amount of time the project should take to complete. Because the time of each activity can vary, however, the projected completion time represents only an estimate. The project may, in fact, require more or less time for completion. The latest expected completion time (TL) refers to the time in which an activity can be completed without delaying the project. To find the values for each activity’s TL, Jim started at activity 8 and set TL equal to the final TE (22 weeks). Next, he worked right to left toward activity 1 and subtracted the expected time for each activity.
The slack time for each activity is equal to the difference between its latest and earliest expected completion times (TL – TE). Figure 3-28 shows the slack time calculations for all activities of the SPTS project. All activities with a slack time equal to zero are on the critical path. Thus, all activities except 5 are on the critical path. Part of the diagram in Figure 3-27 shows two critical paths, between activities 1-2-4 and 1-3-4, because both of these parallel activities have zero slack. In addition to the possibility of having multiple critical paths, two types of slack are actually possible. Free slack refers to the amount of time a task can be delayed without delaying the early start of any task immediately following. Total slack refers to the amount of time a task can be delayed without delaying the completion of the project. Understanding free and total slack allows the project manager to better identify where trade-offs can be made if changes to the project schedule are needed. For more information about understanding slack and how it can be used to manage tasks, see Information Systems Project Management (© 2008) by Mark A. Fuller, Joseph S. Valacich, and Joey F. George (Upper Saddle River, NJ: Prentice Hall).
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