Scope Triangle

Like any human undertaking, projects need to be performed and delivered under certain constraints. Traditionally, these constraints have been listed as: scope, time, and cost. This is also referred to as the Project Management Triangle where each side represents a constraint. This triangle illustrates the relationship between three primary forces in a project. Time is the available time to deliver the project, cost represents the amount of money or resources available and quality represents the “fit-to-purpose” that the project must achieve to be a success. The normal situation is that one of these factors is fixed and the other two will vary in inverse proportion to each other. For example “Time” is often fixed and the “Quality” of the end product will depend on the “Cost” or resources available. Similarly if you are working to a fixed level of “Quality” then the “Cost” of the project will largely be dependent upon the “Time” available (if you have longer you can do it with fewer people).A phenomenon known as “scope creep” can be linked to the triangle too. Scope creep is the almost unstoppable tendency a project has to accumulate new functionality. Some scope creep is inevitable since, early on; your project will be poorly defined and will need to evolve. A large amount of scope creep however can be disastrous. When the scope starts to creep, new functionality must be added to cover the increased scope. This is represented by the quality arm of the triangle, representing the ability of the ‘product’ to fulfill users’ requirements. More requirements fulfilled = a better quality product. In this situation you have three and only three options:1. Add time – delay the project to give you more time to add the functionality2. Add cost – recruit, hire or acquire more people to do the extra work3. Cut quality – trade off some non-essential requirements for the new requirementsIf the art of management lies in making decisions, then the art of project management lies in making decisions quickly! When faced with scope creep you cannot ignore it. You need to tackle it in one of the ways described above (more later) and the sooner the better. Delaying raises the risk of your project failing. A poor project manager will see the scope triangle as a strait-jacket by which their project is irrevocably constrained. A better project manager will make better use of one or more of the axes and will shift the emphasis in the project to one of the other axes. The best project managers will juggle all three like hot potatoes and will make decisions every day which effectively trade-off time vs. quality vs. resources.

The Critical Path

Another important concept in planning projects is that of the critical path. If a project consists of a set of tasks which need to be completed, the critical path represents the minimum such set, the critical set. This might seem to be a contradiction since you might think completion of all tasks is necessary to complete a project; after all, if they weren’t necessary they wouldn’t be part of your project, would they? The critical path represents not the ideal set of tasks to be complete for your project, but the minimum set. It is this path that you must traverse in order to reach completion of your project on time. Other tasks while important to overall completion do not impact upon the final delivery for the project. They can therefore be rescheduled if time is tight or circumstances change. Tasks on your critical path however will affect the delivery time of the project and therefore should only be modified in extremis. In the following example the critical path is represented in bold.

In order to complete my project of cooking breakfast I have to go through the steps of frying bacon and sausages and scrambling eggs. The tasks “make toast” and “wash plates”, while important, are not time-dependent or as critical as the other three tasks. I can move either of those tasks but if I try to move anything on the critical path its going to delay the project. Ideally I’d like to have toast with my breakfast but a) it’s not essential and b) it doesn’t matter where in the process it happens. If I make toast before or after scrambling my bacon, it makes little difference to the overall result. On the other hand I can hardly fry my bacon before the oil is hot, nor can I scramble my eggs before frying my bacon (they’d turn to glue). The critical path represents the critical sequence of events which must occur if I want to successfully complete my project. Normally major 'milestones' will be represented on the critical path and they will often occur when different threads of the project come together. For example in the diagram to the right my only milestone is when I serve the completed breakfast. At this point I will have finished my preparations and completed everything on both tracks. This is represented by a diamond in the diagram above. If I suddenly discovered I was late for work, I could cheerfully discard the optional “toast” component of my project, take the critical path instead and still achieve my original milestone of delivering breakfast (and maybe even make it to work on time!).