What are Task Dependencies in Project Management

in this video want to answer the question what are task dependencies within project management in another video I've made the distinction between internal dependencies and external dependencies and we looked at external dependencies dependencies between your project and things that happen outside of it over which you have no control task dependencies are internal dependencies they're dependencies between things that are happening within your project within your project plan some tasks can happen at any time they are independent of other tasks in fact they don't share resources and they don't have any kind of links you can do them at any time and they are independent but most of the tasks that you'll be doing in your project link to other tasks in some way either they call upon the same or overlapping resources or in logical terms you can't do this task until the previous one has been completed and that's what we mean by task dependencies more formally the term dependency refers to the linkage between tasks the relationship between them and in formal project planning there are four types of tasks dependency and by far the Communist and the most useful is what is called finish to start dependency that is to say that the start of one task is dependent upon the finish of another and that's the kind of logic that you'd expect to arise most often but of course we can also devise other tasks dependencies that are less common for example start to start dependency or which is of course how races are run everyone starts at the same time the start of one runner is dependent upon the start of another thirdly there's finish to finish dependencies where we expect one tasks are finish at time that is determined by the completion of another task and if you think about that lot of cookery and catering depends on finish to finish dependencies you don't want to get one part of the meal ready and then how it's sitting around getting cold while perhaps other parts of the dish are still being completed no you have to plan every component of dish to be ready at the same time that's finish to finish dependency the rarest kind of dependency is start to finish dependency that is to say that the completion of one task needs to be driven by the start of another it's the opposite of finish to start dependency it's unusual and it's often considered bad practice to try to use them in fact in thinking about it always struggle to think of compelling example of start to finish dependency can't think of any logical example that makes sense that will ring true let's take the communist example finish to start dependency to understand little bit more of the jargon the task that comes before the one that needs to finish before the second one can start is usually referred to as the predecessor task and therefore to native english-speakers it won't come as any surprise that the task that comes afterwards is the successor task it's also possible that one task can finish and the next one needs to start but not immediately but with time gap and that time gap between the finisher one task and the start of the next is called lag good example might be painting some would work first you need to put on some primer or an undercoat and of course there is finish to start dependency with the next task of putting on the top coat the finish but you wouldn't expect to complete the task of undercoating or priming your wood and then immediately go on to put on the top coat you need to leave time for it to dry now whilst you could define zero resource dummy task of drying when nobody has to do anything the communist approach is to put in what is called lag and lag is gap between the logical dependencies and the opposite of lag is lead if for any reason you need to link the start of second task to the completion of the first but the second task needs to start before the completion of the first then that's lead if there are different views on good practice in planning and often those are linked most closely to the domain in which the planning is being done and they tend to be stricter firma rules the more critical this type of project you're doing whether it's health and safety criticality or price criticality so it tends to be in the high-end construction industry in military procurements and in complex systems design where there are firm guidelines as to how to use your dependencies in many that I've come across it's viewed that the only dependency you should rely upon is finish to start dependency and everything should be cast in terms of that on the other hand in the recently published APM body of knowledge there's clear statement that the APM considers that lags and leads and start-to-finish dependencies are poor practice whereas the other forms of dependency are considered good practice but of course if you're going to rely entirely on finish to start dependencies you almost certainly will need to be using lags and leads so take your guidance on what is good practice in describing and using task dependencies to drive your plan from the practice within the community within which you're working so that's task dependencies it's the logical linkages between individual tasks and these are internal to your project but vital for creating coherent project plan if you've enjoyed this video please do give us thumbs up and subscribe to the channel indeed why not hit the notification bell to find out about new videos as soon as they arrive in the meantime look forward to seeing you in the next one