The layered architecture is a monolithic architectural style that organizes an application into horizontal layers, each focused on distinct technical concerns.
Understanding the Terms:
- Monolithic application: The entire application is deployed as a single unit.
- Distributed application: Application components are split across different machines and communicate through a network.
- Technical partitioning: Application components are organized based on technical aspects like data access or user interface, rather than business domains.
Layers in the Layered Architecture:
The layered architecture typically consists of three core layers:
- Presentation Layer: Handles external interactions, input and output.
- Business Logic Layer: Encapsulates the core business logic of the application, independent of UI or data storage specifics.
- Data Access Layer: Bridges the gap between the business logic and data storage (database or other mechanisms). It handles data retrieval, manipulation, and persistence.
Architectural Philosophy:
The philosophy behind the layered architecture revolves around two key principles:
Separation of Concerns: Each layer focuses on its specific technical responsibility, preventing overlap and promoting cleaner, more maintainable code. Business logic should strictly reside in the business logic layer, not the presentation layer.
Directed Dependencies: Dependencies flow downward in the hierarchy. Each layer only knows and interacts with the layer directly below it. This minimizes coupling and avoids tangled dependencies when making changes.
- Presentation Layer: Communicates with the business logic layer for processed data and user interaction handling, not directly with the data access layer.
- Business Logic Layer: Receives user input from the presentation layer, applies business logic, and interacts with the data access layer for data needs.
- Data Access Layer: Directly communicates with the database, handling data operations based on requests from the business logic layer.
Following these principles ensures changes in the data access layer implementation are isolated and don’t directly impact the presentation layer. This promotes loose coupling and facilitates easier maintenance and future modifications.
Open Layeres:
While the core principles are crucial, some variations exist. Open layered architecture allows specific layers to interact with non-adjacent layers in the hierarchy, offering:
- Improved performance: Potential performance gains in specific scenarios by bypassing intermediaries.
- Code simplification: Code simplification for complex interactions involving multiple layers.
- Flexibility: More flexibility in specific situations where strict adherence to directed dependencies might hinder development or performance.
However, it also introduces:
- Increased complexity: Openings make the architecture more complex to understand and maintain due to additional dependencies.
- Reduced modularity: Interactions between non-adjacent layers can violate separation of concerns, potentially impacting modularity and reusability.
Implementing Open Layered Architecture:
Implementing an open layered architecture requires careful consideration of trade-offs. Generally, a closed layered architecture is recommended for its benefits in maintainability and understandability. However, in specific scenarios where the advantages outweigh the disadvantages, controlled openings can be strategically introduced with clear documentation and thorough testing.