Ever wished your software had a little more drama—like a blockbuster movie where every twist is recorded for posterity? In the world of software, Events take on that starring role. They capture every memorable moment of your system’s life—think of them as the system’s version of a diary that only talks about the exciting bits. In this article, we’ll explore what an Event is and how these cinematic moments help build systems that are both scalable and fun to maintain.
What Is an Event?
An Event records a past occurrence in a system. Despite various definitions, an Event usually has three key characteristics:
- It is expressed in the past tense.
- It communicates what has happened.
- Its name is descriptive, making the occurrence clear to all who read it.
Event Examples
Consider a local newspaper headline:
Mayor was caught by the police for drinking and driving.
If someone asks, “What happened today?” an event-driven answer might be:
The Mayor was arrested.
This response meets the Event criteria:
- The past tense is used.
- It clearly describes what happened.
- The naming is concise and descriptive.
In computer systems, the same approach applies. For instance, in a user management system, you might encounter events such as:
- User was created
- User was promoted
- User was demoted
Each interaction with a system, whether it updates the state or simply records an action, can be modeled as an Event.
Why Are Events Useful?
Good software design often relies on loose coupling and high cohesion.
Loose Coupling
Loose coupling means that modules do not depend directly on one another. For example, consider a system with a user module and a balance module. When these modules are loosely coupled, the user module does not need to know the inner workings of the balance module. Instead, the balance module simply responds to specific Events related to user actions.
High Cohesion
High cohesion means that related functionalities are kept together in well-defined modules. Organizing code by modules instead of by framework-specific directories makes the structure clear and easier to maintain. Each module acts as a single gateway to the related functionalities, improving both navigability and scalability.
The Problem with Tight Coupling
Imagine a business rule that requires every new user to have an associated balance. In a tightly coupled design, the user creation module might directly call the balance creation logic. Although this works at first, adding more complex rules or additional types of balances can quickly lead to tangled, hard-to-maintain code. This tight coupling makes the system rigid and less able to evolve as business needs change.
Events as a Solution
Events provide a decoupled way to extend system behavior. After persisting a new user, the system emits a “User Was Created” Event. Other modules, like the balance module, can subscribe to this Event and execute their logic based on the new user’s role or requirements. This approach keeps each module independent and the overall system easier to modify when business rules evolve.
Conclusion
In this article, we explored what an Event is, highlighted its core characteristics, and discussed its role in addressing common architectural challenges. A loosely coupled and highly cohesive design makes systems more scalable and easier to maintain. Understanding Events sets the stage for the next step in our tutorial: applying these concepts in an Event Storming workshop.