For many, project management is all about scheduling and for some, scheduling centres around Microsoft Project and Gantt charts. But Project Management Professionals (PMPs)® realise that there is a lot of work to do before a Gantt chart can be considered. Thanks to their PMP® exam training, professional project managers know that Project Schedule Management is based on Project Scope Management and builds on the work done to create the project’s Work Breakdown Structure.
On this page:
- The Role of Work Breakdown Structure (WBS) in Project Scheduling
- Sequencing Activities: Dependencies and Logical Ordering in Project Scheduling
- Resource Constraints and Parallelization in Project Scheduling
- Estimating Durations: Three-Point Estimates for Realistic Project Scheduling
The Role of Work Breakdown Structure (WBS) in Project Scheduling
Without a Work Breakdown Structure (or even an informal Scope Statement), there is nothing to schedule. This makes sense, because the project’s schedule is simply an ordering of the work that needs to be done. If we do not know what we have to do, it becomes extremely difficult to plan when each task has to be done. So the first part of scheduling involves breaking the Work Breakdown Structure beyond its final, Work Package, level – identifying the individual activities that need to be done. The important thing here is to identify activities that can be tracked on a day-to-day basis. You do not want activities that will be estimated in weeks or months. Ideally, these would be measured in hours or, at worse, a few days.
Sequencing Activities: Dependencies and Logical Ordering in Project Scheduling
Having broken the work down into this lowest level, the next step is to sequence the activities. This involves identifying the logical order of business. For instance, we cannot build the walls before the foundation is laid. What we need to consider at this stage are dependencies and there are quite a few to be aware of. We have Mandatory Dependencies. These can be legal or contractual constraints, such as inspections required after certain tasks are complete; or dependencies inherent in the nature of the work – the walls having to be built after the foundations is one of those.
Next come Discretionary Dependencies which actually might not be dependencies at all. They are sometimes called preferred logic or soft logic and represent the traditional way of doing things. If these can be identified, it can be useful when the project manager is putting the schedule together to criticize these dependencies – they might not be needed at all.
External Dependencies most certainly have to be considered and are often beyond our control. Familiar ones include hard deadlines and deliveries from suppliers. Often these dependencies become the anchor points for the project’s schedule. In fact, many project managers like having a hard deadline to aim for, as the scheduling task is now one of fitting in everything so that the deadline is reached. Finally, Internal Dependencies are those within the project’s control and relate to the logical ordering of activities. You cannot test a machine, for instance, until the machine is built. They are, in essence, Mandatory Dependencies that we have placed on ourselves.
The goal of this exercise – what PMPs® call the Sequence Activities process – is to arrange the activities for maximum parallelization. A network diagram showing only the dependencies the laws of physics, the regulatory bodies and our customers place on us is an extremely useful exercise that shows what we could achieve if we had infinite resources at our disposal. Sadly, most project managers do not have this luxury and are faced with assessing every activity on the network diagram and estimating the resources required and the duration it will take.
Resource Constraints and Parallelization in Project Scheduling
Once we start considering resources, more constraints start to emerge. We might have had ten carpentry activities that could, in theory, be done in parallel. However, we have only one carpenter available to do the work. This means that the ten parallel tasks have to become ten sequential tasks. However, if the customer, or our management, is unhappy with the length of the final schedule, we can return to the network diagram and suggest that they give us more carpenters. Carrying out activities in parallel is a great way of shortening the schedule. Identifying where we had to insert resource constraints (Internal Dependencies) can be useful during subsequent negotiations.
People are not the only resources that can add dependencies. The availability of equipment and materials can also delay certain activities. But recognizing these requirements should speed up the Project Procurement Management knowledge area and get orders in for critical supplies as soon as possible.
Estimating Durations: Three-Point Estimates for Realistic Project Scheduling
The last thing to do before embarking on the actual schedule is to estimate the durations of each activity. We strongly recommend using three-point estimates. This approach promotes honesty among the estimators by making contingencies explicit. Instead of asking for an estimate – which is usually framed as: “When will you have that done by?”- the discussion involves asking what the bare minimum time would take, assuming everything went well on the project activity. Then we ask what it would take if everything imaginable went wrong. The difference between the two estimates represents the risk. Analysing the risks and estimating the likelihood of these happening leads to a most-likely estimate.
Having an honest “best case scenario” estimate means that we have set realistic limits on the project schedule. Presenting figures that reflect a scenario where absolutely everything goes according to plan allows the project manager to set the minimum possible project duration. If management insist on going under this, more resources will be required (assuming that you have activities that can be done in parallel). Realistic managers know that there is an element of uncertainty in all projects, so they will appreciate that the most-likely estimate is really the most likely actual result.
Using three-point estimates during the project’s execution will also help in tracking progress. In theory, we should be meeting the optimistic figures. If we are going over these, then some problems have occurred and the project manager can legitimately ask why? This sort of analysis can result in really useful historical data. It also can have the effect of improving performance if the team starts aiming for the optimistic durations rather than the traditional most-likely dates, which have contingency built in.
Velopi’s project management training courses cover all ten knowledge areas, including scope and schedule management. If project management is intriguing for you, you might consider one of our project management professional certification courses that are held online in our virtual classroom. Find out more by visiting our training page or by contacting us directly.