Event Storming: what it is, benefits & risks

1. Right people

The people involved in the Event Storming session are:

Participants. The process must involve both domain experts and people who came to ask questions and be based on cross-department cooperation. Typical participants are C-level employees, stakeholders, business domain representatives, managers, developers, team leaders, designers, and testers, depending on the project’s specifics and objectives. Everyone should be equally engaged, related to the problem, and able to contribute. This usually means involving 6-8 people on average.

The facilitator. To keep an Event Storming session effective, it needs to be led by an experienced facilitator or trainer who plays an essential role in the process. They provide participants with instructions and moderate the entire workshop to make it smooth, clear, and valuable. What’s important, they don’t disrupt the process and don’t interrupt the participants’ vision but only control the flow and make sure it goes in the right direction.

2. Right space

To run an effective Event Storming process, you must prepare the working space.

Start with collecting multicolour sticky notes, markers, and a big piece of paper or a vertically oriented flipchart that will allow you to arrange the notes on the timeline. Make sure you have enough working space, and that you will not be limited by the dimension of the room or paper - as you will prepare a big map containing ideas, expressions, and questions written on sticky notes, the modelling space should be as big as possible. We also advise removing chairs and tables.

Let’s also shortly discuss the colours of sticky notes. To make the process effective, they should appear in different shades. Of course, you can agree on your own colour code within your team, but the most basic colours used in Event Storming are orange, blue, and green. To add more context to the model, you can also use yellow, purple, pink, or red. So, ensure you have enough sticky notes in different colours before setting up the place.

4. Business domain

A good understanding of the business domain is essential in effective Event Storming sessions. There are three main components of the Event Storming model that help to break down the discussed problem:

Events. Identifying domain events is the first step in the process. Domain events are all events that happen and trigger reactions. This step helps to understand the principles and functionality of the designed processes or system and is a critical step of the Event Storming session.

The events, defined and written down on sticky notes, should be then organized in chronological or sequential order on the timeline. The recommended colour of the sticky note is orange, and the phrases should be formed in the past tense to highlight that there are events that actually happened.

The examples of events are:

- An account was created.
- An e-mail was sent.
- Tickets are sold out.
- The payment was completed.

Commands. Once you have your domain events defined, it’s time to evaluate each of them and find answers to the question: why did this event occur? Evaluating each of them will help you to define their causes and the factors that triggered them called commands. They can also represent user interactions with the designed system and are typically written on blue sticky notes.

The examples of commands are:

- Create account.
- Send e-mail.
- Sell tickets.
- Complete payment.

Reactions. The next step in the process is writing down what will happen due to previously defined events. They are put on green sticky notes in the future or present tense.

Examples of the reactions are:

- Creating account results in sending a confirmation e-mail.
- Sending e-mail results in confirming the participation.
- Selling the results of the ticket in blocking the reservation system.
- Completing the payment results in sending an e-book.

Combining events, commands, and reactions helps to map the processes and visualize the functionality of the system.