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Why bother creating a Work Breakdown Structure (WBS)? Why not go straight to a project network and forget the Work Breakdown Structure? The Work Breakdown Structure is needed as it defines all the elements of the project in a hierarchical framework and establishes their relationships to project deliverables. A project is based on information gathered for the Work Breakdown Structure. Hence, the two go hand in hand. Specifically, project networks provide the project schedule by identifying dependencies, sequencing and timing activities, which the Work Breakdown Structure was not intended for. Project networks take time and effort (= money $) to develop. However, the graphical nature of the network shows an easy-to-follow flow and sequence of the work to be done on the project. This, in the end, can save the company much more money than the cost to develop the network. Also, once a network is created, it is easy to modify or change if unexpected events take place. The only case in which a project network may not be necessary is if the project is extremely small, trivial or very short in duration. Why is slack important to the project manager? Slack is an important concept in project management because it tells the manager – after forward and backward passes are calculated – which activities can be delayed. There are two different types of slack: total and free. Total slack is, mathematically, LS – ES, where LS is “late start” and ES is “early start,” respectively. In other words, total slack lets us know the amount of time a particular activity can be put off and not delay the entire project. After slacks for all the activities that comprise the project are completed, we can establish the critical path (CP). The critical path is the network path(s) that has (have) the least slack in common. If you look at the exercises below (it doesn’t matter which one), you can see that the critical path is highlighted in red. Notice that the slack values for all nodes in the critical path are 0. Hence, this is the critical path because it is the path with the least slack in common. The other type of slack is free slack. Mathematically, free slack is ESBB - EFAA. That is, the “early start” of activity B minus the “early finish” of the preceding activity, A. An activity with free slack can be delayed w/o delaying the ES of succeeding activities. Slack is, therefore, paramount for knowing the critical path. Once the critical path is known, time and resources can be tightly managed and costly mistakes can me minimized or eliminated. If some unexpected delay does arise in the critical path, it is possible to identify the activities on the critical path that cost the least to shorten. Activities on others paths may also need to be shortened. Explain why adding manpower to a project running late makes it later? This concept holds very true in the real world of projects. If there is a rush to meet the project deadline, Project Managers may add additional manpower to activities occurring towards the end of the project network. However, there is a learning curve! The new people assigned to the activities have to be trained, inter-personal relationships have to be developed, etc. This takes time (which is contrary to what the Project Manager is trying to do). The concept of additional communication (delaying the project) can be explained this way: Two People = 1 line of communication Hence, adding manpower increases lines of communication, which costs precious time. Adding other resources (besides people) late in the game has similar consequences. Say, the deadline to a project is approaching and certain critical activities need to have their durations shortened. Therefore, a new, faster software program is purchased and installed in an attempt to decrease the maximum crash time. However, the new software will take time to install and learn (another learning curve). So, adding a resource late in the project life cycle will make it later.
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