Project Management

[ Project Management Topics ]

Precedence Relations

Precedence

When one task must be completed before another task can be started, the first task is said to have precedence over the other.

Precedence Relationship

The term used in the precedence diagramming method for a logical relationship. In current usage, however, precedence relationship, logical relationship, and dependency are widely used interchangeably regardless of the diagramming method in use.

There are four forms of precedence relationships:

  1. Start of activity depends on finish of preceding activity, either immediately or after a lapse of time
  2. Finish of activity depends on finish of preceding activity, either immediately or after a lapse of time
  3. Start of activity depends on start of preceding activity, either immediately or after a lapse of time
  4. Finish of activity depends on start of preceding activity, either immediately or after a lapse of time.

Precedence Diagramming Method (PDM)

A network diagramming technique in which activities are represented by boxes (or nodes). Activities are linked by precedence relationships to show the sequence in which the activities are to be performed.

diagram

Arrow Diagramming Method (ADM)

A network diagramming technique in which activities are represented by arrows. The tail of the arrow represents the start and the head represents the finish of the activity (the length of the arrow does not represent the expected duration of the activity). Activities are connected at points called nodes (usually drawn as small circles) to illustrate the sequence in which the activities are expected to be performed:

diagram

diagram

Images taken from http://www.mindtools.com/pages/article/newPPM_04.htm