Every system has a story. A thing happened. Then another thing happened. Then a user reacted. Then the system responded. It's a timeline — but most architectures throw that timeline away the moment they overwrite a row in a database.

Event Sourcing is the idea that you stop throwing it away. You record what happened, immutably, in order. Your state becomes a consequence of your history, not a replacement for it. You get time travel. You get a full audit log. You get the ability to build an entirely new view of your data from events that already exist.

But here's the part most teams miss: Event Sourcing doesn't automatically make your system understandable. The gap between business intent and technical implementation is still there — and it's still expensive.

That's where Event Modeling comes in.

Event Modeling gives your entire team — developers, domain experts, product owners — a shared visual language to describe how a system behaves before anyone writes a line of code. It uses exactly three building blocks: commands, events, and read models. It uses exactly four patterns. That's it. You can explain the whole approach in ten minutes. The rest you learn by building.

In this talk, I'll walk through what it actually looks like to go from a domain brainstorm to a running, event-sourced application — using Cratis, an open-source event sourcing platform for .NET, and Cratis Studio, a collaborative modeling tool that takes your event model and generates type-safe C# commands, events, and projections directly from your design.

Design and code that tell the same story. No translation loss. No "it made sense in the meeting" moments two sprints later.

You'll see:

- How Event Modeling forces clarity about what your system actually does
- Why Event Sourcing is the natural implementation layer for a model-first approach
- How code generation from a shared model eliminates the drift between design and reality
- What time-travel debugging and projection replay look like in practice

This isn't a theoretical talk. We'll go from blank canvas to working software — live.