Network Definitions

Before studying the development of network, it is essential to have an idea about the basic concepts and terms involved in the technique as explained below:
Project: It is a task with defined objective.
Network: A network is a graphic representation of all activities and events that must be completed to reach the end objective of a project, showing the planned sequence of their accomplishments, their precedence relationships and interdependencies. Thus the basic components of a network are events and activities.
Event: An event is a specific accomplishment, physical or mental, in a project. The main characteristics of an event are.
It is recognizable at a particular instant of time, which is a point in time and not a passage of time.
It does not, therefore, consume time or resources.
It is represented on a network by a geometrical figure such as a circle.
It expresses a state of being, such as: contract awarded, project approved, plant commissioned etc.
Activity: An activity represents a job or a project element to be completed. It is a relationship between two events and usually devotes the efforts required to perform a task measured in terms of elapsed time. The characteristics of an activity are:
It usually consumes time and resources.
It is represented on the network by an arrow, the direction of arrow indicating the sequence in which the events are to occur.
It must be independent i.e. each arrow is used to represent exactly one, and only one, operation of segment of an overall programme.
It indicates works, such as: preparation of decision, scrutiny of tenders, etc.
Predecessor Event: An event which restricts or precedes another. It establishes the starting point of an activity.
Successor Event: An event which succeeds another. It establishes the termination point of an activity.
Objective Event: An event which has no successor event. It is the goal of the project and usually has a committed date.
Activity Duration: The time required to perform an activity on a network is termed as activity duration. It is the time estimated for performing that activity. It is desirable that the time estimates of an activity should be :
1. made by personnel most familiar with the individual activities and responsible for their accomplishments
2. based on normally available and expected resources, and
3. expressed in suitable times such as days/weeks.

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