2.2 + 5.2+ 1.0 + 3.0 + 5.5+1.3
Start-to -Fin ish
Start-to -Fin ish
Figure 7.5 PDM Relationships tested after it is written. Or, in other words, the code is written and then tested. This relationship is similar to the successor and predecessor relationships used in the AON method.
Start-To-Start (SS)—A start-to-start relationship between tasks or activities occurs when two tasks can or must start at the same time. Although the tasks start at the same time, they do not have to finish together—i.e., the tasks can have different durations. A start-to-start relationship would be one type of parallel activity that can shorten a project schedule. Finish-To-Finish (FF)—Another type of parallel activity is the finish-to-finish relationship. Here, two activities can start at different times, have different durations, but are planned to be competed at the same time. Once both of the FF activities are completed, the next activity or set of activities can be started, or if no more activities follow, the project is complete.
• Start-To-Finish (SF)—The start-to-finish relationship is probably the least common and can be easily confused with the finish-to-start relationship. A SF relationship, as illustrated in Figure 7.5, is exactly the opposite of a FS relationship. In addition, a SF relationship means that task A cannot end until task B starts. An example of a SF relationship in real life might be a nurse working at a hospital. This person may have to work until they are relieved by another nurse who arrives to start the next shift.
An advantage of using PDM is that the project manager can specify lead and lag times for various activities. More specifically, lead time allows for the overlapping of activities. For example, a project plan may have two activities or tasks that have been identified as a finish-to-start relationship. These two activities may be the setup of computers in a lab followed by the installation of an operating system on those computers. If we had two people, one to set up the computers and one to install the operating systems on each computer, the project plan might specify a finish-to-start relationship where the installation of the operating systems cannot begin until all of the computers have been set up in the lab. Based upon this project plan, the person who installs the operating system must wait and watch while the other person works.
Let's assume, however, that it takes about half the time to install an operating system as it does to set up a computer. Furthermore, there is no reason why the software person cannot begin installing the operating system when the hardware person has about half of the computers set up. In this case, both tasks will finish about the same time, and we have created an opportunity to shorten the project schedule. By scheduling the task of installing the operating systems when the task of setting up the computers is fifty percent complete, we have used the concept of lead time to our advantage.
On the other hand, let's suppose further that before our hardware person starts setting up the computers in the lab, we want the lab walls to be painted. This would be another finish-to-start relationship because we would like to schedule the painting of the lab before we start installing the computers. Using lead time in this case, however, would not make sense because we do not want the hardware person and painters getting in each other's way. In this case, we may even want to give the freshly painted walls a chance to dry before we allow any work to be done in the lab. Therefore, we would like to schedule a lag of one day before our hardware person starts setting up the computers. Another way of looking at this is to say we are going to schedule a negative lead day in our project schedule.
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What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.