middlelayer

Middle layer, commonly referred to as the middle layer or business logic layer, is a software tier positioned between the presentation layer (user interface) and the data layer (databases and repositories). It is responsible for implementing the core rules and workflows of an application, coordinating tasks, transforming data between UI and storage representations, and enforcing security and validation at the business level.

Its typical duties include enforcing business rules, orchestrating interactions among multiple components or services, handling transactions, performing data validation, applying authorization decisions, coordinating error handling and logging, and providing APIs or services to the presentation layer.

In three-tier architectures, the middle layer sits between the UI layer and the data access layer. It may be realized as a set of services or objects, often organized around domain concepts. It can assume responsibility for mapping between domain models and data transfer objects, interfacing with repositories, and encapsulating external service calls. In modern systems, the middle layer is frequently implemented as a service layer within a monolith or as a set of microservices that expose clear interfaces.

Benefits include separation of concerns, improved maintainability, easier testing, and the ability to reuse business logic across different UIs and clients. Potential drawbacks are added complexity and potential performance overhead if the layer becomes too fat or poorly designed.

Note on terminology: middlelayer is sometimes used interchangeably with middle tier or service layer, but it should not be confused with middleware, which refers to connecting and integrating disparate systems at a lower level such as messaging, data transformation, or protocol bridging.