In this chapter, we've learned about complex event processing and its relation to Drools. CEP can provide a lot of value to make complex decisions on a large number of events for the same reasons Drools is a great tool for making fast reliable decisions. We've seen the use of time and length-based sliding windows, temporal operators, and entry points.

We've also seen how to declare our events from new classes, declared types, and existing types. We've covered a few examples of rules for fraud detection cases and how they align with CEP principles. Among these principles, we've also briefly discussed event-driven architecture, a very useful design for applications that need to focus on CEP solutions.

In the next chapter, we will start looking into defining our rules in more user-friendly ways by studying how to define rules in natural language and decision tables.