Time Management : Precedence Diagram Method or Activity on Node

Time management: Precedence diagramming method (PDM) or activity-on-node (AON)
This is a tool to draw network diagram for the time management in project management. In this method activities are placed at the nodes and arrows are used to show the dependence of the activities. Activities can have four types of dependencies discussed below
Finish-to-start: An activity must finish before the next activity can start. This is the most common form of dependence. E.g. you must construct building before you can start the painting of the walls.
Start-to-start: An activity must start before the next activity can start. E.g. you must start the design before you can start coding for the software.
Finish-to-finish: An activity must finish before the next activity can finish. E.g. testing of the software should finish before the finish of the documentation or the installation of the software.
Start-to-finish: An activity must start before the next activity can finish. This kind of dependency is not common. E.g. ignition of the explosive should start before the old building can be collapsed using explosive.
Activities can be sequenced using any of the following kind of the dependencies
Mandatory dependency: These are the dependencies that are inherent in the nature of the work or are required by the contract of the work.
Preferential dependency: These are the dependencies set by the project manager. These can be changed by the project manager if there are change request for any reason from any of the stakeholder of the project. This gives freedom to the project manager to crash the schedule of the project.
External dependency: These are the dependencies set by the stakeholders or the government and have to be met by the project manager to satisfy the requirements of the projects.