What is the role of the domain layer in application architecture?

The domain layer in application architecture is responsible for business logic and domain rules. It encapsulates core entities, their behaviors, and interactions, independent of technical implementation details such as databases or user interfaces.

Role of the domain layer:

• Representing key business concepts through models and objects.
• Implementing business rules and logic that ensure data and process correctness.
• Ensuring independence of business logic from infrastructural layers (e.g., UI, databases).
• Simplifying testing of business rules without the need to involve external components.

For example, in an online store application, the domain layer may contain classes like Order, Product, Customer with methods for calculating order cost, checking product availability, etc. This layer should not know how data is stored or displayed to the user — its task is solely business logic.