CQRS — Command Query Responsibility Segregation — A Java, Spring, SpringBoot, and Axon Example

The term "CQRS" or "Command Query Responsibility Segregation" was first introduced in 1997 by Bertrand Meyer in his book "Object-Oriented Software Construction" as "Command Query Separation." It was later introduced as CQRS by Greg Young in 2010. This architecture is designed to address the issues of object-oriented architecture, specifically the different loads and security concerns between read and write operations. CQRS is also a form of domain-driven design, where applications are divided into bounded contexts, each with its own set of concerns and data handling requirements. In a CQRS model, commands are operations that can mutate data without returning a value, while queries are operations that never mutate data and always return values. The implementation of CQRS can involve the use of event sourcing and separate databases for read and write operations, allowing for better performance and data handling.