Posted by SkillMaker in Jan, 2017 Show
What are Project Management Task dependencies?Task dependencies (sometimes called logical relationships) are the interrelationships between tasks on a project. These dependencies fix the order in which activities are carried out. For ease of explanation, the dependencies that exist between tasks will be described in terms of just two: the predecessor task (the one before) and the successor task (the one with which the predecessor has a relationship). They are typically shown in a GANNT Chart. Four types of task dependencies
What causes Project Management Task dependencies?Dependencies are created for different reasons. The constraints may be:
Parent–child relationships Another type of task relationship is the parent–child relationship. This relationship is not a dependency, though there may be dependencies between the various child tasks. It exists when a large task (the parent) is broken down into its various smaller (child) tasks. Displaying task dependencies The dependencies between tasks, as represented on a GANTT Chart, will show some activities following one another, others occurring in parallel, and others starting or finishing within a time range set by another activity. This means there are often gaps of time between tasks. Sometimes, these time gaps are set delays— for example, lag time, whereby a certain amount of time, say 2 days, has to elapse after Task A starts (say, allowing a first coat of paint to dry) before Task B (applying a second coat of paint) can start. Other time gaps, such as lead time and float, allow the Project Manager to exercise flexibility in determining when they will be scheduled. Identifying the critical path Once a project schedule is developed, showing all task dependencies, resources can be meaningfully appointed to particular tasks, and the critical path for the project can be identified, using tools such as Critical Path Method, PERT or the Critical Chain Method. Additional resources To see an explanation of task dependencies and lag time, view: https://www.youtube.com/watch?v=moKzeG42Dpw In project management, all tasks have dependencies. If they didn’t they wouldn’t be part of the project. That is, a task that doesn’t need to be completed in order to finish the project is not part of the project. It’s an orphan adrift at sea. There are four types of task dependencies, and each one has its own specific reason why you would use it.
Finish-to-Start (FS)In this relationship, task B cannot start until task A finishes. This is the most common scenario and in the absence of any other criteria, all tasks could have this dependency in order to produce a functioning schedule. For example,
Finish-to-Finish (FF)In this relationship, task B cannot finish until task A finishes. For example,
Start-to-StartIn this relationship, task B cannot start until task A starts. For example,
Start-to-FinishIn this relationship, task B cannot finish until task A starts. This is a rare relationship but it happens:
Each task should have two relationships:
The Critical Path MethodOnce all the tasks in the project have their relationships established, the critical path method can be used to determine the minimum and maximum project completion dates, as well as float times for each task. Task floats allow the project manager to see how far ahead or behind schedule a task can be without affecting the overall completion date. Dependencies ExampleIn a hypothetical house building project, the dependencies would be listed on a predecessor table, like this:
Notice a few things:
Mandatory vs. Discretionary DependenciesUntil now we have dealt only with mandatory dependencies, which is when the task relationships are physically absolute, or mandated by contractual or legal requirements. You can also define discretionary dependencies, in which the relationship is not set in stone. Why would you want to do that?
Using most project management software you can specify discretionary dependencies and monitor progress against a “preferred” versus a mandatory schedule. External vs. Internal DependenciesDependencies also fall under the categories of Internal vs. External.
External dependencies should be avoided. Many projects require approval from regulatory agencies or other external parties, and the addition of a task, let’s say “Environmental Review” places the project in the unenviable position of being dependent on a third party. You have to put a duration on the task, but how are you to know how long it will take the third party that has little interest in whether you meet your project’s schedule or budget? Unfortunately this is a common situation and the budget and duration (and any other project ramifications) must be estimated conservatively with appropriate contingencies. During the project the third party task must be actively managed. When they miss their deadline and cause the project to change, the resulting changes must be communicated to stakeholders expeditiously. Leads and LagsSometimes there need to be gaps between tasks.
In theory, leads and lags are the same thing except for the direction from the reference point. A lead is simply a negative lag, and vice versa. It’s like using the identical terms height and depth. In Project management software, you often have to enter leads as negative lags, because lags are more common. All Tasks Should have a DependencyThe Project Management Body of Knowledge (PMBOK) states that all tasks should have a dependency. This is because by definition, if a task is part of a project it must be related to other tasks in some way. For example, the Eat Dinner task cannot start until Cooking is complete. Of course, it is possible to draw a graphical schedule containing a bunch of tasks without any relationships between them, but this is a hypothetical scheduling exercise. Professional project management requires the rapid determination of schedule impact from the many situations that occur during the project (not to mention effective project control). Put another way, if you cannot answer the following questions you haven’t used project scheduling to its full capability:
Since projects are always changing and monkey wrenches have a pesky way of getting into the best laid plans, it is important to have a realistic and achievable schedule. Which means the tasks should have relationships to one another. What is the most common type of task dependency?Tasks may have multiple preceding tasks and multiple succeeding tasks. The most common dependency relationship is a finish-to-start relationship.
What task relationship is the most common one?The most common relationship is the Finish to Start relationship. It is pretty logical as a predecessor task A must be finished before successor task B can start.
Which type of dependency is most common in project schedules?FS [Finish-to-Start]
This is the most commonly used dependency in project management. It's when project managers finish a project task before they start another one.
What is task dependency?Task Dependency is a relationship in which a task or milestone relies on other tasks to be performed (completely or partially) before it can be performed. This is also referred to as a logical relationship.
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