When building an Event Sourcing system, can we change the past? Can we also forecast “events” in the future?
If we want to provide various projections/visions of things that hapenned over the time, what are the consequences and trade-offs on our code?
All these questions will be answered during this talk. But moreover, I'll tell you our learning story about Bi-temporal Event Sourcing. Yet another illustration of the power of modeling, sketches and concrete examples when we need to understand each others.

Creating multiple models for the same problem is one of the more important lessons that Domain Driven Design teaches us. It is a lot cheaper to quickly iterate over them and throw away less useful prototypes before we even start coding. However, creating multiple models can be hard. When we begin gaining insight from our domain, we suffer a lot from cognitive biases that get in our way to gain new insights. We need these insights before we even start thinking about modelling. Tools like event storming and example mapping can help us to deliberate discover, and battle these biases. They help you quickly gain insight into the problem space. But the fallacy here is that we can get locked into the tool, and get stuck again.

What you will learn
In this workshop, you will learn the essentials of event storming and how it can help you gain the necessary insights you need to deliver quality software. With our newly acquired domain knowledge, we can then start exploring the solution space. During the exploration, we begin to design and model multiple models for the same problem with Domain Driven Design patterns. This way of visualising gives us the power to quickly iterate over the different models and figure out which model will be the best to use for now. Eventually, we start our coding journey TDD style, iterating over the model to refactor towards deeper insights while discovering how hexagonal architecture may help us to protect our domain code from the technical concerns, in the long run.

Target Audience
This workshop is for you if you are a software architect or software developer.

Introduced by Eric Evans in 2004 via his Blue Book, Domain Driven Design (DDD) has received tremendous positive feedbacks from many developers & communities over the years. On the other hand, we have to admit that DDD has since not been widely used in the trenches or within most of our development projects... How can we explain such failure in its diffusion? Is DDD in itself difficult or is it just the way people used to present it which makes it hard to grasp and inaccessible?
Through our various (more or less successful ;-) experiences, we will try to highlight what DDD is using a simple and more accessible approach. The opportunity for us is to show you how helpful it can be for your day-to-day projects. Wouldn't be the perfect time for all of us to ease the DDD onboarding for beginners and to reboot DDD for experts?

Why we are still stuck with TDD nowadays? Through several facts & stories from the trenches, we will see why most of us still have not managed to grasp or to sustain the TDD experience.

Wouldn't be a good opportunity to meditate about how we are thinking? And why not, thinking outside of the box to get a better feeling of the TDD soul.