Networks are diagrams easily visualized in transportation system like roads, railway lines, pipelines, blood vessels, etc.
A project will consist of a number of jobs and particular jobs can be started only after finishing some other jobs. There may be jobs which may not depend on some other jobs. Network scheduling is a technique which helps to determine the various sequences of jobs concerning a project and the project completion time. There are two basic planning and control techniques that use a network to complete a pre-determined schedule. They are Program Evaluation and Review Technique (PERT) and Critical Path Method (CPM). The critical path method (CPM) was developed in 1957 by JE Kelly of Ramington R and M.R. Walker of Dupon to help schedule maintenance of chemical plants. CPM technique is generally applied to well known projects where the time schedule to perform the activities can exactly be determined.
An activity is a task or item of work to be done, that consumes time, effort, money or other resources. It lies between two events, called the starting event and ending event. An activity is represented by an arrow indicating the direction in which the events are to occur.
The beginning and end points of an activity are called events (or nodes). Event is a point in time and does not consume any resources. The beginning and completion of an activity are known as tail event and head event respectively. Event is generally represented by a numbered circle .The head event, called the jth event, has always a number higher than the tail event, called the ith event, ie., j > i.
Activities which must be completed before a particular activity starts are called predecessor activities. If an activity A is predecessor of an activity B, it is denoted by A<B. (i.e.,) activity B can start only if activity A is completed.
An activity that cannot be started until one or more of the other activities are completed, but immediately succeed them is referred to as successor activity.
Network is a diagrammatic representation of various activities concerning a project arranged in a logical manner.
A path is defined as a set of nodes connected by lines which begin at the initial node and end at the terminal node of the network.