The project manager’s guide to activity sequencing
November 30, 2022
When following a recipe for a cake, you can’t just fling every ingredient in a bowl and hope for the best — you need to follow the instructions in order, or you’ll end up with a mess. The same is true for project activities in a project. If you want to finish your project on time and within budget, you need to sequence them correctly, or the results will be unpredictable.
Sequencing project activities may seem daunting, but it’s easy once you understand the basics. We’ll walk you through the basic steps, then share some tips for ensuring everything runs as smoothly as possible.
What is activity sequencing in project management?
In project management, activity sequencing is the process of identifying and scheduling the individual activities that make up a project. Sequencing activities logically ensures that all the necessary steps happen correctly and helps you optimize resources efficiently.
Key terms used for activity sequencing
Before we get into how to do this, there are some key terms you need to know.
A dependency is a relationship between two or more activities where the start or finish of one activity depends on another activity’s start or finish. In other words, one activity cannot begin until another activity has finished. For example, if you’re painting a room, you can’t paint the walls until you’ve finished plastering them.
Predecessor and successor
A predecessor is an activity that must finish before another activity can begin; a successor is an activity that can’t begin until another activity finishes. In our earlier example, the predecessor task would be plastering the walls, and the successor task would be painting them.
Lag and lead time
Lag refers to any delay time. Using our example: if one of the team members is off sick and plastering gets pushed back a day, that’s a lag time of one day.
Lead time refers to how long you have to complete an activity without impacting other jobs. Again using our example, say painting can’t begin until five days after the plastering is complete, but you start plastering three days early. That’s a lead time of three days.
Why sequencing is so important when planning project activities
Here are three reasons why sequencing matters:
1. It ensures that the necessary steps happen in the correct order. Missed or delayed tasks can jeopardize a whole project.
2. It helps you optimize resources. Efficiently allocating scarce resources ensures everyone has what they need to do their job effectively.
3. It allows you to identify potential bottlenecks early on. Planning ahead means identifying areas where delays or problems could occur over time. You can then use this information to develop a contingency plan.
How to sequence project activities
There are a few different tools you can use to sequence project activities, including Gantt charts, the PERT charts, and the precedence diagramming method (PDM). Since we’ve already covered the first two in-depth, we’ll focus on the PDM today.
PDM is a graphical representation of the relationships between tasks. It’s often used with the critical path method (CPM) to schedule projects. The diagrams consist of ‘nodes,’ which represent tasks, and linking arrows, which represent dependencies.
To create a PDM, you first need to identify all the activities, tasks, and subtasks that form the project (top tip: a work breakdown structure, or WBS for short, can help you here). Once you have a complete list, you can start establishing the relationships between each. But before we get into task relationships, let’s look at the three stages that go into sequencing.
Define activity attributes
First, you need to define the attributes for each activity, including the activity name, description, predecessor, successor, and lag and lead time.
Then, you need to identify any constraints that could impact the project schedule. Constraints include things like resource availability, regulatory requirements, and contractual obligations. Remember to consider both internal and external influences.
Finally, you need to establish the dependencies between activities. As we mentioned earlier, a dependency is a relationship between two or more activities, where one activity’s completion is dependent on another activity’s completion. We’ll talk a bit more about this in the next section.
The four types of dependencies in project sequencing
Four types of relationships can exist between two tasks:
- Finish-to-start (FS): This is the most common type of relationship, and it means that one task must end before another task can begin. In our earlier example, plastering the walls must be finished before painting can begin.
- Start-to-start (SS): This type of relationship means that two tasks can start simultaneously. For example, plastering the walls can happen at the same time as the outside wall is being rerendered.
- Finish-to-finish (FF): This type of relationship means that the successor activity cannot finish until the predecessor activity has finished. For example, you must finish writing a blog post (predecessor) before editing (successor activity) can finish.
- Start-to-finish (SF): This type of relationship is less common. It means that one task must start before another task can finish. For example, you’ll need to open a new bank account (successor) before you close the old one (predecessor).
How to create a precedence diagram
Once you have defined your activity attributes, constraints, and relationships between tasks, you can begin the PDM.
- Create a task list
Gather all your tasks and subtasks together, and identify which are preceding activities, and which are their predecessors.
- Identify dependencies
Now it’s time to identify all the possible dependencies that form your project. You might want to get other team members to help you out here, since they’ll almost certainly spot connections you may have overlooked. This is an important step in the PDM, and missing out on a key dependency could cause big scheduling problems.
- Put this information in a diagram
Now it’s time to add your nodes and arrows. Remember:
- each task = a node;
- each arrow = a dependency.
Place the very first activity/task on the left, then add the second, connected via an arrow. If the following tasks share a predecessor, stack the nodes on top of each other, with multiple arrows originating from the predecessor.
Free sequence diagram template available in Cacoo
Ideally, you’ll want to use diagramming software for this task. Not only do templates make the creating side of things a whole lot easier, but having it all online means you can edit, share, and store it online.
- Add information to the nodes
Next, annotate the node with activity information, including duration. You can also add things like lag and lead time, float and slack, earliest finish time and latest finish time.
Best practices for sequencing project activities
Here are a few pointers to help you on your way.
Establish the relationships between tasks early on
The sooner you can establish the relationships between tasks, the easier it will be to create an accurate schedule.
Use PDM in conjunction with CPM
PDM is a great tool for creating a network diagram, but it can be difficult to use on its own to generate a critical path. CPM is a more sophisticated scheduling technique that takes into account things like resource availability and task dependencies.
Be flexible with the schedule
No project is set in stone. Things will inevitably come up that can throw off the schedule, so it’s important to be able to adapt. Our top tip: Use online tools, like Cacoo, to make editing and updating your diagrams easy.
Consider your team’s schedule
When you’re creating a project schedule, it’s important to take into account the availability of your team members. You need to make sure that you assign tasks in a way that doesn’t overwhelm any one member of the team. It can be helpful to create a responsibility assignment matrix (RAM) to keep track of who is responsible for what.
Know the difference between mandatory constraints vs. discretionary constraints
Mandatory constraints are things like regulatory requirements or company policies that must be adhered to. Discretionary constraints are things like preferences or best practices that aren’t required but are still worth considering.
Create a task list before you begin sequencing
It’s no secret project managers have a lot on their plate. It can be helpful to create a task list before you start sequencing activities. This will help ensure nothing important slips your mind.
Use software to help you sequence activities
There are lots of tools out there, but some are better suited to network diagrams than others. With Backlog, you can create Gantt charts, burndown lists and track task relationships from one place.
Sequencing project activities is an important part of project planning, and by following these tips, you can get the most out of your efforts. To make the job easier, we recommend using tech to do the heavy lifting. Try cloud-based diagramming tools to create a range of editable and shareable diagrams; chat apps for remote collaboration; and project management tools to keep your activity list up-to-date.