Understanding Software Architecture: Concepts, Layers, and Design Principles

Software architecture refers both to the structural organization of a system (noun) and the process of designing and evolving that structure (verb). It consists of several elements: the overall system, subdivided into modules, which contain components, and the relationships (associations) among them; larger systems may also be organized into subsystems.

Vertical architecture emphasizes layering, a timeless design principle that separates concerns into distinct layers. Typical three‑layer architecture includes Presentation, Business Logic, and Data Access layers, each with specific responsibilities and clear interfaces, improving organization, maintainability, and testability.

For larger applications, a four‑layer architecture may add a foundational layer, while horizontal architecture focuses on modularization and decoupling between business modules to control complexity as the app scales.

Complexity can be quantified by counting module dependencies; decoupling via an additional API service layer can dramatically reduce complexity, as illustrated by the before‑and‑after diagrams.

Architecture design should follow three principles: suitability (choose appropriate vertical/horizontal designs for the business), simplicity (prefer simpler solutions when they meet requirements), and evolution (continuously refine and adapt the architecture as the product grows).

Design patterns and SOLID principles are applied after the architectural shape is defined; for example, introducing an abstraction layer to decouple user and message modules demonstrates the Dependency Inversion Principle.

Cross‑platform and dynamic considerations also impact architecture: UI cross‑platform solutions (WebView, Weex, RN, Flutter) trade performance for flexibility, while C++ cross‑platform approaches offer performance at the cost of higher development complexity.

In summary, architecture describes the structural elements of an app, serves as a verb for the design methodology, and must adhere to suitability, simplicity, and evolution principles to remain effective as the system grows.

Further reading includes case studies of QQ client architecture evolution and performance engineering, as well as links to detailed articles on architectural design principles.