Understanding Task Dependencies in Project Management

Dependencies are the relationships among tasks which determine the order in which activities need to be performed. There are four (4) types of dependency relationships.

Types of dependencies                                                                    

Finish to StartFinish to StartPredecessor must finish before Successor can start. [Land must be purchased before road building can start]
Start to StartStart to StartPredecessor must start before Successor can start. [Road excavating must start before Asphalt can be laid]
Finish to FinishFinish to FinishPredecessor must finish before Successor can finish. [Laying Asphalt must be complete before line painting can be completed]
Start to FinishStart to FinishPredecessor must start before Successor can finish. [Road excavating must start before line painting can be completed]

Dependencies are the relationships of the preceding tasks to the succeeding tasks. Tasks may have multiple preceding tasks and multiple succeeding tasks. The most common dependency relationship is a finish-to-start relationship. Task P (predecessor) must be finished before task S (successor) can start. The least common relationship is the start-to-finish relationship. Project Insight, project management software, supports all four dependency relationships.

Product Development Activity List

Activity List With Task Dependencies

The chart above shows how a Product Development Activity List may look after the project team determines the task relationships. In our example, only finish-to-start relationships were used.

It is always easier to arrange all tasks in terms of a finish-to-start relationship and an ‘as soon as possible’ constraint. This dependency type is the easiest relationship for others to understand and will usually result in a longer than normal schedule. This gives the schedule more ‘slack.’ You may then utilize the other relationships as ways to shrink the duration of the overall schedule.

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