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Unformatted text preview: cy. Things are not always this simple. There are other types of dependencies between two tasks A and B that can occur, such as start -toend dependencies, start -to-start dependencies, and end-to-end dependencies. Precedence diagrams are well suited for representing these other types of dependencies. Figure 2-10 represents a fragment of a precedence diagram for the tasks that appear in Figure 2-7. The relationship between the Clear & Grub task and the Grading task is a simple end -to- Figure 2-10. An example of a precedence diagram. Page 43 start relationship, that is, the Grading task cannot start until the Clear & Grub task is finished. However, the relationship between the Clear and Grub task and the Earth Removal task is what is called a start-to-start relationship. This means that the Earth Removal task can begin (a certain fixed lag time) after the Clear & Grub task starts. The relationship in Figure 2-10 between the Mesh Installation task and the Anchor Bolts task is an example of a finish-to-finish relationship. What this means is that the Anchor Bolts task must finish within a fixed lag time after the Mesh Installation task finishes. There is no example of a start-to-end relationship in Figure 2-10. A start-to-end relationship between tasks A and B is one in which task B must finish within a fixed time after task A starts. Start-to-end relationships are not as common as the other types of relationships. Nonetheless, they occur occasionally on many projects. Sequencing the work is ordinarily an iterative process. It is often undertaken by a group of project team members on large projects. Precedence diagrams are constructed and then reviewed and discussed among the group. An automated scheduling tool is often helpful in generating these work sequencing diagrams. But, just because a scheduling tool is used, we should not confuse these sequencing diagrams with a project schedule, even if they are used in such a way as to produce (putative) start and end dates for the individual tasks. It is not unusual for construction of work sequencing diagrams to cause the project management team to rethink the very nature of some of the work packages and tasks. In fact, it is a process that often helps validate the subdivision of work. It is often found that problems in the sequencing of the work can be solved by changing the decomposition of the work into different work packages and tasks. Changes in the subdivision of work leads to changes in quantification, which in turn leads to changes in the sequencing. This is not a never-ending process, however. Usually, one or a few iterations serve to produce a meaningful sequencing of the work. Such a sequencing gives Page 44 confidence to the project manager that the work is really subdivided in a manner that can be executed in a timely fashion. 2.5— Budgeting (Estimating) the Work The next step in project planning is to establish a project budget. To do this, an estimate of the laborhours and the cost for each...
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This note was uploaded on 01/11/2011 for the course ACC 9 taught by Professor Yeetan during the Spring '10 term at Sunway University College.
- Spring '10