Project Management, Task Dependencies

Establishing task dependencies is important in developing a project network diagram because it will help

* to define the sequencing of the tasks:

o which are the tasks that have to be done before task X can start

o and which are the tasks that cannot be started before X is finished

* to define which are the tasks that can be done simultaneously: X and Y can be started at the same time because none of them need the deliverable of the other task to start

When all those dependencies have been established a project network can be designed.

The project network diagram is a tool to determine the:

* the period of time in which each task has to be done

* the critical path: "the sequence of schedule that determines the duration of the project". (PMBOK, 2008, p. 431)

The critical path indicates the earliest date of completion of project. On this path, any task not finished on time could delay the whole project. This path has to be closely monitored by the project manager. But "The critical path is dynamic in nature and may change, or shift, frequently" (Furniss & Trauner, 2010, p.6). That means that monitoring those tasks is not enough, an eye has to be kept on the other tasks as well as the situation can change and the critical path can also change.

In our textbook, Wysocki says that "four types of constraints will affect the sequencing of projects tasks: technical (discretionary, best-practices, logical and unique), management, interproject and date constraints" (Wysocki, 2009, p. 167)

Logically, there can be four types of dependence between two tasks:

FS, Finish-to-start: the first task has to be finished before the next can start

SS, Start-to-start: the second one may start once the first one has started

FF, Finish-to-finish: the second one cannot be completed before the first one

SF, Start-to-finish: the first one cannot be finished before the second one has started

The most commonly used is the finish-to-start while the start-to-finish is rarely used.

Understanding the constraints is compulsory to define exactly the type of dependencies and thus define the right place of all tasks in the program network diagram.

Based on a request for quotation, here is a simple example to illustrate the types of dependence and the constraints. The boundaries of the process are the decision to launch the tender and the award. The tasks are: