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Risk management - Dependencies - 4 basic types

Dependencies - 4 basic types

Preparing a schedule risk analysis is very similar to that for the cost.
Certain aspects are different. For example, where the total cost is basically a summation of a list individual task costs a schedule summary relies on the relationships between the tasks.

These relationships are called LINKS and will lead to a NETWORK of tasks.
This data is often managed by suitable scheduling software (for example, Microsoft Project) to prepare the overall schedule, identify the critical path and ascertain the final completion date.

Tasks are linked by 4 basic types:

Finish to startThis is by far the most common. Task A must finish before Task B begins. e.g. the primer paint coat must be completed before the finish coat is applied.
Start to finishThis is rare. It is often complicated to put into a schedule and is best substituted by Finish to Start with suitable lags. Task A must start before Task B can finish. e.g. this may could apply if completion of task B relies on materials or equipment that require a period of preparation (task A) and it is important that they are prepared just ahead of requirement.
Finish to finishQuite common. Task A and Task B finish at the same time (or strictly Task A has to finish before Task B can finish). This is useful if you have two or more activities running in parallel that rely on some common element to finish at the same time. e.g. two reports can not complete until they receive a common piece of information.
Start to startQuite common. Task A and Task B start at the same time (or Task A has to start before Task B can start). e.g. Both tasks await the arrival of a common component before manufacturing can start or a decision point has been reached and tasks A and B cannot proceed until a decision has been made.

Task dependencies are tricky and need a lot of thought for the final schedule. Tasks very commonly have dependencies on many tasks. Often tasks do not fit neatly into the above brackets. Task lags are often used, both positive and negative. See next for examples as displayed in MS Project [see Dependencies - 4 basic types part 2].