---
title: Concepts
description: "Concepts behind event-sourced systems: event sourcing, CQRS, event stores, event modeling, projections, read models and event-driven architecture."
---

These pages explain the ideas behind event-sourced systems, independent of any product. Each one defines the concept, shows how it works, gives a short example, and says when not to use it. Examples use [Chronicle](/chronicle/) and [Arc](/arc/) so you can see the idea in real code.

| Page | Question it answers |
| --- | --- |
| [What is event sourcing?](/concepts/event-sourcing/) | What does it mean to store changes as events instead of current state? |
| [CQRS explained](/concepts/cqrs/) | Why separate the model that changes data from the model that reads it? |
| [Event store vs. a regular database](/concepts/event-store/) | How is a database built for events different from a relational or document database? |
| [Event modeling: a practical guide](/concepts/event-modeling/) | How do you design an event-sourced system before writing code? |
| [Projections and read models](/concepts/projections-and-read-models/) | How do events become queryable views? |
| [Event-driven architecture vs. event sourcing](/concepts/event-driven-architecture/) | How do messaging between services and event storage relate? |

Start with [what is event sourcing?](/concepts/event-sourcing/) if the terms are new. When you are ready to build, continue with [Get started with Chronicle](/chronicle/get-started/) or the [Cratis Stack overview](/cratis-stack/).