Project Management

[ Project Management Topics ]

Duration & Network Diagrams

Duration

Duration is the length of time it will take to complete the project or components of the project. In some cases you will experience duration compression, which is the shortening of the schedule without reducing project scope. In most cases this requires additional project cost.

Usually duration is developed when you are estimating the cost of the project. A common terminology is to use effort to define the number of people-hours needed to do a particular task. It is the length of time it takes to do a task whether it is one person or more than one.

Span, on the other hand, is the time that elapses between the start and the finish of the activity.

So for example if we have:

Monday: Mary and Mark
Tuesday: Jane
Wednesday: Leroy and Bruce

The duration is three days, the span is three days, and the effort is five people-days. If we have:

Monday: Mary and Mark
Wednesday: Jane
Friday: Leroy and Bruce

The duration is still three days, but now the "span" is five days, and the effort is five people-days.

Network Diagram

A network diagram, as defined by Wideman, is:

• A schematic display of the sequential and logical relationship of the activities which comprise the project. Two popular drawing conventions or notations for scheduling are arrow and precedence diagramming.
• A view of project data in which the project logic is the sole determinant of the placements of the activities in the drawing. Frequently called a flowchart, PERT chart, logic drawing or logic diagram.
• A graphic representation of activity sequence and relationships. Activity boxes are connected together with one-way arrows to indicate precedence. The first activity is placed on the left side of the diagram with the last activity on the right side. Activity boxes are usually placed at different levels (not in a single row) to accommodate activities that are done simultaneously.

Once we have the durations and logic of a project we can actually build a schedule. Here are the steps advised by Newell (p. 57):

1. Create a list of activities that are to be scheduled
2. Assign a duration to each of the activities
3. Determine the predecessor for each activity
4. Calculate the forward pass, the early schedule for each activity
5. Calculate the backward pass, the late schedule for each activity
6. Calculate the float for each activity
7. Determine the critical path
8. Determine if the predicted project completion is ealier than the promise date
9. Adjust schedule or promise date
10. Apply resources and determine resource constraints
11. Adjust the schedule to allow for resource constraints
12. Determine if the predicted completion is ealier than the promise date
13. Adjust schedule or promise date
14. Get approval on schedule.

Precedence Network 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.

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:

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

 

----- REFERENCES -----

Newell, M. W. (2002). Preparing for the Project Management Professional (PMP) Certification Exam. New York, NY: American Management Association.

Project Management Institute (2000). A Guide to the Project Managment Body of Knowledge. Newton Square, PA: Project Management Institute, Inc.