Why Classification Thinking Is the Core of Application Architecture

Classification Thinking in Application Architecture

Modules, components, and packages are familiar concepts for developers, but understanding their deeper purpose reveals that classification thinking is the core of application architecture. By grouping software at different granularities, we keep complex systems understandable and maintainable.

Why Classification Matters

Human brains naturally categorize information because short‑term memory can hold only about seven items. Grouping reduces cognitive load, enabling us to analyze differences and synthesize commonalities.

Key Concepts

Application : A system composed of multiple modules.

Module : A collection of components, represented as a cube.

Component : An independent functional unit, shown in UML component diagrams.

Package : An organizational form that can contain multiple components and vice versa.

Elements of Application Architecture

Architecture can be defined as a structure composed of components, their relationships, and guiding principles. Enterprise applications typically follow a three‑layer model: frontend, backend, and database.

COLA’s Four‑Layer Structure

The COLA framework advocates a four‑layer structure that maps to Maven modules, each producing a JAR:

<modules>
    <module>cloudstore-adapter</module> <!-- Adapter layer -->
    <module>cloudstore-app</module>      <!-- App layer -->
    <module>cloudstore-domain</module>   <!-- Domain layer -->
    <module>cloudstore-infrastructure</module> <!-- Infrastructure layer -->
    <module>cloudstore-client</module>  <!-- RPC SDK -->
    <module>start</module>               <!-- SpringBoot entry -->
</modules>

This layered approach controls complexity compared to a monolithic design.

Evolution from COLA 3.0 to 3.1

COLA 3.0 introduced interceptors, event bus, and extension points, but many were over‑engineered. COLA 3.1 removed the rarely used features, refined the packaging strategy, and expanded the responsibilities of the controller (now called Adapter) to support multi‑endpoint scenarios.

Packaging Strategy

Instead of purely functional packaging, COLA recommends domain‑oriented packages. This improves understandability and eases future splitting of complex domains.

Better system comprehensibility and maintainability.

Facilitates independent evolution of domains (e.g., extracting an Order domain).

Adapter Replaces Controller

Traditional MVC controllers are web‑centric. With the rise of mobile and other clients, an Adapter layer better matches the Hexagonal Architecture’s driving adapters, handling routing, request adaptation, and technology‑specific concerns.

Organizational Analogy

Just as Apple’s functional‑plus‑business organization aligns with COLA’s physical (functional) and logical (business) divisions, effective classification in both software and companies leads to better alignment with core competencies.

Conclusion

Classification is both a science and an art; there is no universally best way, only the most suitable one for a given context. The COLA framework exemplifies how thoughtful classification and packaging can evolve to meet changing technical and business needs.

For more details, visit the COLA GitHub repository .