Project scheduling is the mechanical process of formalizing the planned functions, assigning the start and end dates to each task or activity of the work in such a manner that the whole work (project) proceeds in a logical sequence and an orderly and systematic manner.
Scheduling is the sequencing of the activities of the project in the time order in which they are to be performed, and calculating the resource requirements (men, machine, material, money) needed at each stage of production/construction along with the expected completion time of each of the activity.
Project Schedule Techniques
The Project Planner graphically represents project schedules. Several methods are available, including Bar charts, Milestone Charts, CPM, PERT, and Precedence Networks. Nowadays industries rely on software for Project Scheduling, better known as MSP and Primavera.
All the above-listed techniques will be described in detail in this post and forthcoming posts.
I. Bar Charts or Gantt Charts
The simplest and most commonly used scheduling technique is the Bar Chart or Gantt chart. It was introduced by Henry Gantt around 1900 AD.
The chart consists of a horizontal scale divided into time units like days, weeks or months and a vertical scale showing project work elements like activities, tasks or work packages.
Please refer to the figure for more understanding
The Gantt chart is prepared after a WBS analysis and Work Packages or other tasks are identified. During WBS analysis, the Project Planner/Manager plans the estimated times for each activity/task.
Bar charts were later modified into Milestone charts. While the Bar chart represents the activities, a milestone chart represents the events which mark either the beginning or the end of an activity.
II Network Diagrams
The network diagram is an outcome of the improvements in the milestone charts. Network technique is based on the basic characteristics of all projects, that all work must be done in well-defined steps. The network technique exploits these characteristics by representing the steps of the project (activities/tasks)graphically in the form of a network or arrow diagram which resulted in two types of network –a) Activity on Arrows (AOA) b) Activity on Nodes(AON)
The AOA and AON network techniques were a result of two significant developments in the field of Project Management in the 1950- PERT and CPM.
- Program Evaluation and Review Technique( PERT)
PERT was developed to aid in producing the U.S. Polaris missile system in record time in 1958. The PERT procedure provides a probability that a project will be completed on or before a specified completion date based on variable time estimates of activity durations. The PERT system uses a network diagram consisting of events which must be established to reach project objectives. An event is that particular instant of time at which some specific part of a plan is to be achieved. It indicates a point in time and does not require any resources. PERT uses event-oriented network diagrams in which successive events are joined by arrows. PERT is an AON type of network.
Terms of PERT/CPM
Activity : Activities are the recognizable jobs or operations which use resources (men, machines, materials, money & time).
Example –For laying a foundation the activities will be
Event: Events are the state resulting from the completion of one or more activities. It is the instant of time when certain activity has been started or completed. Events consume no resources or time.
•Side boards fixed
PERT system is preferred for those projects or operations which are of non-repetitive nature for those projects in which precise time determination for various activities cannot be made.
2. Critical Path Method (CPM)
CPM network also known as Activity on Arrow, the whole project consists of a number of clearly recognisable jobs or operations called activities. Activities are usually operations which take time to carry out, and on which resources are expended. Connections between activities are termed events.The CPM networks are often referred to as activity-oriented diagrams in which each activity is represented by an arrow and the sequence in which the activities are executed is shown by the sequence of the arrows.
•Predecessor activity: Activity or activities that are required to be performed before an activity under consideration.
•Successor activity: Activity or activities that are required to be performed after completion of an activity under consideration.
•Dummy Activity: A dummy is a type of activity in the network which neither requires any time nor resources. A dummy is used to prevent two arrows from having common beginning and end events. A dummy is used to give a logical clear representation in a network having an activity common to sets of operations running parallel to each other. A dummy is thus a connecting link for control purposes or for maintaining the uniqueness of the activity. A dummy is represented by a dotted arrow in a network and is identified by the numbers of the terminal node.
Drawing of Network
Example 1: Draw a network diagram for the project having 9 activities, with the following inter-relationships:
•C follows D but precedes F
•C follows A but precedes H
•G follows F but precedes I
•E follows B but precedes I
•D follows B
•H and I terminate at the same time
•A and B start at the same time.
Example 2: A project consists of six activities (jobs) designated from A to F with the following relationships:
1 A is the first job to be performed.
2. B and C can be done concurrently and must follow A
3. B must precede D
4. E must succeed C, but it cannot start until B is complete.
5. The last operation F is dependent on the completion of both.