Network Building
Blocks
We will use the components shown in Figure 7-1 as the building blocks in our schedule network.
As seen there, we have the simple task, the simple path consisting of at least two tasks in tandem, the parallel paths
consisting of two or more simple paths joined by a milestone, links between
tasks, and milestones that begin, end, and join paths. To simplify
illustrations, the milestones are often omitted and are simply implied by the
logic of the network. For instance, as shown in Figure 7-2, we see the task itself serving as the
starting, ending, and joining mechanism of tasks.
There are certain characteristics that are applied to each
schedule task, represented by a rectangle in our network building blocks. These
task characteristics are:
-
Every task has a specific beginning and a specific ending,
thereby allowing for a specific duration (ending date minus beginning date)
measured in some unit of time (for instance, hours, days, weeks, or months).
Rarely would a schedule task be shown in years because the year is too coarse a
measure for good project planning.
-
Every task has some effort applied to it. Effort is measured
in the hours spent by a "full-time equivalent" (FTE) working on the task. By
example, if the effort on a task is 50 hours, and a FTE is 40 hours, then there
is 1.25 FTE applied to the task. If the task duration is 25 hours, then the 50
hours of effort must be accomplished in 25 hours of calendar time, requiring 2.5
FTE. Thus, we have the following equations:
-
FTE applied to task = (Effort/Duration) * (Effort/Hours per
FTE)
-
FTE applied to task = (50/25) * (50/40) = 2,500/1,000 =
2.5
-
Every task has not only a specific beginning or ending, but
also each task as an "earliest" or "latest" beginning or ending. The idea of
earliest and latest leads to the ideas of float and critical path, which will be
discussed in detail subsequently. Suffice it to say that the difference in
"earliest" and "latest" is "float" and that tasks on the critical path have a
float of precisely
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