- Scheduling Assessment Criteria
- Describe ways to create and maintain a schedule (including critical path and Gantt charts);
- Differentiate between critical path and critical chain as a scheduling
In this podcast, we examine the steps involved in developing a project schedule, the advantages and disadvantages of using software tools to develop a project schedule and the different forms of presentation that can be used to display a project schedule. This podcast is part of our APMP project management training course. This includes a printed study guide, on-line e-learning and face to face workshop.
Scheduling Assessment Criteria
By completing this sub-section you will be able to:
- describe ways to create and maintain a schedule (including critical path and Gantt charts);
- differentiate between critical path and critical chain as a scheduling technique
Importantly these assessment criteria apply to both linear and iterative cycles.
Describe ways to create and maintain a schedule (including critical path and Gantt charts);
Scheduling starts once we have completed the definition of the scope in terms of the products to be delivered and the work required to produce them. You can learn more about how to define the scope in this post here: A complete guide to project scope.
From here, we can create the schedule using either iterative or linear approaches. Our aim is to produce a schedule baseline for the deployment phase of the project, what the APM call a deployment baseline. There are two approaches, one for linear lifecycles and one for iterative lifecycles. You can learn more about deployment baselines for linear and iterative lifecycles in the video below.
Creating the schedule for linear lifecycles.
To create a schedule for a linear lifecycle project, we have several approaches critical path and critical chain.
Critical Path Scheduling
The most common is the critical path and most commonly represented by the ‘red line’ on a Gantt chart. The critical path is defined by the APM as
Critical path A sequence of activities through a precedence network from start to finish, the sum of whose durations determines the overall duration.Project management Glossary | Terms used by project professional (apm.org.uk)
Or alternatively, the long path through the project activities. To create the critical path the project needs to follow these steps.
- Develop a precedence diagram which typically defines what must be completed before an activity can be started, often called project dependencies. So, for example, we cannot build the walls of a house before the foundations. This will involve working with the project team to map out the dependencies between each of the activities. This can be an extremely valuable excise because it often will flush out new and unexpected dependencies between the different teams.
- Once we have the critical path, we then need to determine the duration of these activities using our normal estimating techniques. This can include parametric, analytical or analogous estimating techniques normally applied to cost. So for example, we can estimate the duration of an activity based on the quantity of work, the working rate and the efficiency of the team.
- Calculate the early/starts and finishes and late starts/finishes for each activity using critical path analysis. We use a forward and backwards pass to perform these calculations. For very small projects, these calculations can be done by hand or in excel. For larger projects, project managers often use a tool such as Microsoft Project or similar planning software to do these calculations.
- From these calculations, we can determine what is the critical path or longest path through the project and also the floats on the non-critical tasks. It is often worth reviewing the critical path to see if these results are as expected could the critical path be reduced by completing tasks in parallel. Would a change in the method have a significant impact on reducing the duration of the critical path, for example, maybe off-site manufacturing or using commercially available standard components?
- The final step may be to add resources to the schedule to work out how many people are required of each skill type and when. When doing this is is important to understand how flexible the resources are on the project. Which activities require specialists and constrained resources. So, for example, a specific type of software engineer or someone authorised to approve part of a design. If necessary, we can undertake some resource smoothing or levelling.
A refinement of this approach is critical chain scheduling
Just draw a Gantt Chart
Another common way to create a schedule is just to draw a Gantt chart in a tool like Excel or PowerPoint. Nowadays, there a many simple templates and tools that enable to create a great looking simply and quickly. This will make many project controls professionals and project planners wince, but for may simple project this is a sufficient solution. Especially if the project only has a few activities and milestones. Many project managers I meet draw the a Gantt chart without using any critical path analysis. It’s simple, quick, easy and looks good. However, it’s harder to maintain and update.
How to maintain the schedule for a linear lifecycle.
To maintain a project schedule project managers need to
- Update the schedule with progress information. This is most commonly done by updating the percentage of complete data for each of the activities and milestones. Typically this is updated once a week or month, depending on the pace of the project. Critical to the success of this step is getting reliable and accurate progress information from team members.
- The schedule will need to be updated with changes agreed as part of the change control process. Any approved changes will need to be incorporated into the project schedule and the schedule re-baselined and issued to team members. Part of the problem is that changes to the plan may be delayed by commercial discussions about who will pay for the change. This can make the plan meaningless if these discussions become protracted.
- The third change is re-planning, this is taking the plan within the agreed targets to reflect new detailed information about the resources and approach to the project.
Creating a schedule for iterative lifecycles
An iterative lifecycle has fixed duration iterations, typically between 4-6 weeks each. These are also called sprints. They are most commonly used in software development projects. The APM defines an iterative lifecycle as:
Iterative life cycle A life cycle that repeats one or more of the phases of a project or programme before proceeding to the next one with the objective of managing uncertainty of scope by allowing objectives to evolve as learning and discovery takes place.Project management Glossary | Terms used by project professional (apm.org.uk)
So the deployment baseline or schedule for an iterative lifecycle is very simply a set of fixed time periods. Typically a project will plan several of these to complete the project. So we might have 8 iterations of 4 weeks each. As a project manager we would need to consider:
- How many iterations should be planned and how long these iterations should last
- What skills and resources should be committed to each iteration. For example, we may need data scientists early in a development cycle to define the core algorithms to be used, more database development engineers as the project reaches maturity and we get ready to scale up to a larger user community.
Differentiate between critical path and critical chain as a scheduling
The APM defines critical chain scheduling as:
Critical chain A resource-based approach to scheduling, useful when time is critical and derived from the critical path, that protects critical chains of activities with buffers.Project management Glossary | Terms used by project professional (apm.org.uk)
Critical chain is a development of critical path method. Put in simple terms, it has two differences from critical path
- It recognised resource dependencies. This means that resources can not be working on the same activity at the same time. Hence these activities are linked sequentially even if there is no dependency between them other than the fact they share a resource.
- Buffers are created by extracting contingency from individual tasks. In critical chain take any contingency time out of individual activities and use this to create a buffer (or shared contingency) at the end of the project. This is supported by a change in working. No longer do people have to deliver to fixed dates, rather, they have to apply full-time effort to the activities. You can think of this as a accelerated schedule for the team members with the contingency owned by the project manager.
We have another video that explains the critical chain method in more detail.
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