CHAPTER ONE INTRODUCTION
A project defines a combination of interrelated activities that must be executed in a certain order before the entire task can be completed. The activities are interrelated in a logic sequences in the sense that some activities cannot start until others are completed .An activity in a project is usually viewed as a job requiring time and resources for its completion .In general ,a project is a one time effort !that is, the same sequence of activities may not be repeated in the future. In the past ,the scheduling of a project "over time# was done with little specifies the start and finish for each activity on a hori$ontal time scale . Its disadva disadvanta ntage ge is that the interd interdepen ependenc dency y between between the differ different ent activi activitie ties"w s"whic hich h mainly mainly controls the progress of the project#cannot be determined from the bar chart .The growing complexities of today%s project have demanded more systematic and more effective planning techniques with the objective of optimi$ing the efficiency of executing the project .&fficiency here implies effecting almost reduction in the time required to complete the project while accounting for the economic feasibility of using available resources . 'roject management has evolved as a new field with the development of two analytic technique for planning, scheduling, and controlling of projects. These are the critical path method "(')# and the project evaluation and review technique "'&*T# the two techniques were developed by two different groups almost simultaneously "+-/ +-0#(') was first developed by &.Idu 'out de 1emours and company as an application to cons constr truc ucti tion on proj project ectss and and was was late laterr exte extende nded d to a mo more re adva advance nced d stat status us by )auc )auchly hly associates . '&*T , on the other hand was developed for the 2.3. 1avy by a consulting firm for scheduling the research and development develop ment activities for the 'olaris missile program. '&*T and (') are basically time oriented methods in the sense that they both lead to the determination of a time schedule . Although the two methods were developed independently , they are strikingly similar . 'erhaps the most important difference is that originally the time estimates for the activities were assumed deterministic in (') and probabilistic in '&*T. Today , '&*T and (') actually comprise one technique and the differences , if any,are only historical . (onsequently , both techniques will be referred referred to as 4project scheduling4 techniques.
'rojec 'rojectt schedu schedulin ling g by '&*T '&*T/(') consis consistt of three three basic basic phase, phase, planni planning, ng, 3chedul 3cheduling ing,, and controlling. The planning phase is initiated by breaking down the project into distinct activities . The time estimates for these activities are then determined and a network "or arrow#diagram is constructed with each of its arcs"arrows# representing an activity. The entire arrow diagram gives a graphic representation of the interdependencies between the activities of the project. The construction of the arrow diagram as a planning phase has the advantage of studying the different jobs in detail .perhaps suggesting improvement before the project is actually executed . )ore important will be its use to develop a schedule for the project. The ultimate objective of the 3cheduling phase is to construct a time chart showing the start and finish times for each activity as well as its relationship to other activities in the project. In addition, the 3chedule must pinpoint the critical "in view of time# activities that require special attention if the project is to be completed on time. 5or the non critical activities the schedule must show the amount of slack or float time that can be used advantageously when such activities are delayed or when limited resources are to be used effectively . The final phase in project management is project control .This include the use of the arrow diagram and the time chart for making periodic progress reports. The network may thus be updated and an
The *eliable (onstruction (ompany has just made the winning bid of 6-.7 million to construct a new plant for a major manufacturer. The contract includes the following provisions8 A penalty of 69::,::: if *eliable has not completed construction within 7; weeks. A bonus of 6+-:,::: if *eliable has completed the plant within 7: weeks
Activity
Activity Description
Immediate Predecessors
A
&xcavate
<
Estimated Duration (Weeks =
>
?ay the foundation
A
7
(
'ut up the rough wall
>
+:
@
'ut up the roof
(
&
Install the exterior plumbing
(
7
5
Install the interior plumbing
&
-
'ut up the exterior siding
@
;
B
@o the exterior painting
&,
I
@o the electrical work
(
;
C
'ut up the wallboard
5, I
0
D
Install the flooring
C
7
?
@o the interior painting
C
-
)
Install the exterior fixtures
B
=
1
Install the interior fixtures fixtures
D, ?
The latest start time for an activity is the latest possible time that it can start without delaying the
completion of the project "so the finish node still is reached at its earliest finish time#. The latest .finish time has the corresponding definition with respect to finishing the activity ?3 E ?atest start time for a particular activity ?5 E ?atest finish time for a particular activity ?atest .5inish Time *ule8 ?5 E 3mallest ?3 of the immediate successors 'rocedur 8e for obtaining latest times for all activities 5or each of the activities that together complete the project "including the finish node#, set ?5 equal to &5 .of the finish node 5or each .activity whose ?5 value has just been obtained, calculate ?3 E ?5 duration 5or each new activity whose immediate successors now have ?3 values, obtain its ?5 by applying ap plying the .latest finish time rule. Apply step = to calculate its ?3 *epeat .step 9 until ?5 and ?3 have been obtained for all activities
