Task dependencies and their role in in developing a project network diagram

The project network diagram is the visual presentation- a graph- of all tasks in the project, or one of the workstreams of a project, and their relation to each other. The project plan, when presented graphically, will create the project network diagram.

In order to demonstrate the project plan or workstream plan in a graphic way, i.e. in order to create the project network diagram, the links between the tasks need to be identified and defined. Each individual or multiple tasks are related to each other, and therefore, must be performed in a particular sequence (Luecke, 2004). This requirement for a sequential completion is called a dependency. Dependencies are created by the constraints which exist between the tasks.
There are four types of inter-task constraints, as identified by Wysocki. First are the technical constraints- these are the basic relations between the tasks, when the completion of one (outcome) allows the next task to begin. There is no flexibility when the technical constraint links the tasks- they must be completed in a certain sequence. The tasks linked by the technical constraint usually create a critical path of the project. The second are the management constraints- when the management makes a decision to hold off one process or another, in anticipation of some changes, or pending a result of decisions, processes or events. The management constraints are reversible, i.e. the management can change their decisions. Third type of constraints are the interproject constraints. These are similar to technical constraints: the results of the tasks from one project are required in order to complete the tasks from the second project. The last type, are the date constraints. There are three different date constraints: the task cannot end earlier than the specified date, the task cannot end later that the specified date and the task must finish on the specified date. The date contraints limit the project schedule flexibility.
Before creating a project schedule, the dependencies between tasks need to be specified, and to do so, project manager needs to determine the constraints linking the tasks. Once this is done, the tasks can be arranged in the logical order and that way, the sequence is created.
The technical and interproject constraints influence the order in which the tasks occur, i.e. which tasks are precedent, which need to follow and which cannot occur without the others being completed.
The date constraints will determine the timeline for the tasks and allow the project manager to arrange the tasks in the logical order.
The management constraints require further planning from project manager, as he or she needs to prepare the contingency, in case a management takes the decision to hold off the process or reschedule it.

References:
Wysocki, Robert K. “Effective Project Management: Traditional, Agile, Extreme”; 5th edition; Wiley Publishing Inc .; Indiana; 2009
Luecke, Richard “Managing Project Large and Small. The Fundamental Skills for Delivering on Budget and on Time”; Harvard Business Essentials; Harvard Business School Press; Massachusetts; 2004

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