In software engineering, layered architecture is a common design pattern that divides different parts of an application into different layers, each with specific responsibilities and functions. One of the main principles of this architecture is that each layer can only couple to the layer below it to reduce the interdependence between layers. Based on the traditional layered architecture, there are two main types of layered architecture: strict layered architecture and loose layered architecture.
Strictly layered architecture is a very common architectural style that strictly stipulates that a layer can only be coupled to the layer directly below it. The advantage of this architecture is that it can significantly reduce the coupling between layers, making each layer more independent. However, it also brings certain limitations, which may hinder the coupling between layers. Interaction and communication.
In contrast, a loosely layered architecture is more flexible, allowing any upper layer to be coupled to any lower layer. The advantage of this architecture is that it can improve the interactivity between layers to better support the development of distributed systems and large-scale applications. But at the same time, it may also increase the coupling between layers, making the independence between layers worse.
In DDD (Domain-Driven Design), traditional layered architecture is widely used. The following figure is a schematic diagram of a typical DDD traditional layered architecture, which divides different parts of the application into four layers: user interface layer, application layer, domain layer and infrastructure layer. Each level has its own responsibilities and functions. Let’s introduce this layered architecture in detail.
The user interface layer is the layer responsible for processing user requests and user display. It usually includes web interfaces, mobile applications, desktop applications, etc. The main responsibility of this layer is to provide a user interaction interface, receive user input and requests, and present the processing results to the user.
The application layer is the layer that implements use cases or business processes in different business scenarios. Application services usually receive requests from the user interface layer, obtain aggregate instances through the resource library, and then execute corresponding command operations. The main responsibility of this layer is to provide functions such as business logic processing and service invocation for applications, and to encapsulate business rules, processes and logic in this layer.
The domain layer is the layer responsible for implementing the business domain model and business rules. This layer usually includes concepts such as entities, value objects, services, and aggregations. It encapsulates business logic and data in the same domain model, achieving unified management of business logic and data.
The infrastructure layer is a layer that provides technical support for other layers. This layer usually includes public services such as data access, message queues, caches, and logs to provide infrastructure support for other layers.
In summary, traditional layered architecture plays an important role in application design. By dividing the application into different layers, each with its own responsibilities and functions, the coupling between layers can be significantly reduced and the independence and maintainability between layers can be improved. At the same time, this layered architecture also helps developers conduct independent development and maintenance at different levels, thereby improving development efficiency and code quality.