Resource scheduling is a collection of techniques used to analyse the resources required to deliver the work and when they will be required. The goals of resource scheduling are to ensure:
- efficient and effective utilisation;
- confidence that the schedule is realistic;
- early identification of resource capacity bottlenecks and conflicts.
Resource scheduling is a supplement to time scheduling, not an alternative. The procedure has three steps:
The model developed in the time scheduling function is used as the basis for allocation of resources to different components of work. This enables the demand for resources to be aggregated over time. This almost inevitably leads to a demand profile that has periods where demand exceeds supply or where resources are idle. The purpose of calculating the schedule, using resource limited scheduling techniques, is to modify timings in order to deal with these peaks and troughs of demand.
From a scheduling point of view there are two broad categories of resource – consumable and reusable. Consumable resources are typically materials. Reusable resources are people and machinery.
The first step in the procedure allocates resources to activities. This will comprise quantities of consumable resource or the effort required by re-usable resources. Once the resources have been allocated and a time schedule calculated, the resources can be aggregated. The results of aggregation are normally presented as a resource histogram. For consumable resources the histogram will normally show cumulative usage (also known as an s-curve). For reusable resources the histogram shows usage period by period (i.e. day-by-day, week-by-week or as required).
The schedule for consumable resources forms the basis of procurement including detail that may be included in a contract, such as the scheduling of deliveries. The schedule may also reveal issues with materials or components that have to be ordered well in advance. This can sometimes lead to the situation where orders need to be placed before the work is fully authorised (see the ‘pre-authorisation work’ activity in the definition process).
Reusable resources are rarely, if ever, limitless and the schedule needs to be reviewed to take all limitations into account. There are two approaches to resource limited scheduling that reconcile resource limits and time constraints: resource smoothing (or time limited resource scheduling) and resource levelling (or resource limited scheduling).
Resource smoothing reschedules activities while retaining the finish date calculated by critical path analysis. This results in a resource histogram where the peaks and troughs are ‘smoothed out’ but not eliminated. A smoothed schedule is useful where it is possible and practical to procure additional resources for periods of time.
Resource levelling ensures that resource demand never exceeds availability. This usually results in an increase in the time taken to complete the work and is more appropriate when there are strict limits on the available resources.
The simple process of smoothing or levelling the whole schedule (‘simple’ because it is the default approach of most scheduling software packages) does not reflect the true situation. In reality, some resources may have flexibility while others do not meaning that some need to be smoothed and some need to be levelled. It is also a fact that the schedule will be more sensitive to limits on some resources than others, but this effect is masked when all resources are scheduled simultaneously.
A better understanding of the relationship between resource limitations and the schedule can be achieved through a form of sensitivity analysis where resources are scheduled individually. Alternatively, techniques such as critical chain can be used to address the issues in a different way.
Projects, programmes and portfolios
Most resource limited scheduling techniques are based on an initial model based on a network diagram. The drawbacks of scaling these techniques from projects up to programmes and portfolios are explained in time scheduling.
Once the overall schedule for a programme or large complex project is broken down into component schedules, each one can be analysed locally. Of course, the problem here is that local decisions may have a wider impact that is then lost. A balance must be found between creating an overly large and detailed schedule that no-one can effectively manage and a series of local schedules that do not reflect all the inter-dependencies.
Where the work is sufficiently large or complex to warrant multiple schedules the programme or portfolio management team should focus on capacity planning. In general management, capacity is defined as ‘the maximum amount of work that an organisation is capable of completing in a given period’.
A programme or portfolio management team must therefore consider the capacity of the resources available to their work. They may adopt a policy of allocating portions of these resources to the component projects where the detailed scheduling is done. The component schedule may then be consolidated for review and the process repeated until a balance of resource distribution is achieved. This is part of the balancing activity in the portfolio management process.