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Part Three
Planning and control
Critical commentary
When project managers talk of ‘time estimates’, they are really talking about guessing.
By definition, planning a project happens in advance of the project itself. Therefore, no
one really knows how long each activity will take. Of course, some kind of guess is needed
for planning purposes. However, some project managers believe that too much faith is
put in time estimates. The really important question, they claim, is not how long will something
take, but how long could something take without delaying the whole project. (We
deal with this issue partially when we discuss the concept of float later in the chapter.)
Also, if a single most likely time estimate is difficult to estimate, then using three, as one
does for probabilistic estimates, is merely over-analysing what are highly dubious data
in the first place.
Identify relationships and dependencies
All the activities which are identified as composing a project will have some relationship with
one another that will depend on the logic of the project. Some activities will, by necessity,
need to be executed in a particular order. For example, in the construction of a house, the
foundations must be prepared before the walls are built, which in turn must be completed
before the roof is put in place. These activities have a dependent or series relationship. Other
activities do not have any such dependence on each other. The rear garden of the house could
probably be prepared totally independently of the garage being built. These two activities
have an independent or parallel relationship.
Example project
Table 16.2 identified the activities for the breakfast preparation project. The list shows that
some of the activities must necessarily follow others. For example, ‘boil egg’ cannot be carried
out until ‘fill pan with water’ and ‘bring water to boil’ have been completed. Further logical
analysis of the activities in the list shows that there are two major ‘chains’, where activities
must be carried out in a definite sequence:
Slice bread – Toast bread – Butter toast
Fill pan with water – Bring water to boil – Boil egg
Both of these sequences must be completed before the activity ‘take loaded tray to bedroom’.
The remaining activities (‘pour orange juice’ and ‘fetch tray, plates, cutlery’) can be done at
any time provided that they are completed before ‘take loaded tray to bedroom’. An initial
project plan might be as shown in Figure 16.9. Here, the activities have been represented
as blocks of time in proportion to their estimated durations. From this, we can see that the
‘project’ can be completed in nine minutes. Some of the activities have spare time (called
float) indicated by the dotted line. The sequence ‘Fill pan – Boil water – Boil egg – Bedroom’
has no float, and is called the critical path of the project. By implication, any activity which
runs late in this sequence would cause the whole project to be delayed accordingly.
Identify schedule constraints
Once estimates have been made of the time and effort involved in each activity, and their
dependencies identified, it is possible to compare project requirements with the available
resources. The finite nature of critical resources – such as special skills – means that they
should be taken into account in the planning process. This often has the effect of highlighting
the need for more detailed replanning. There are essentially two fundamental approaches: 8
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Resource-constrained. Only the available resource levels are used in resource scheduling,
and are never exceeded. As a result, the project completion may slip. Resource-limited
scheduling is used, for example, when a project company has its own highly specialized
assembly and test facilities.