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C4 Model

The C4 model for software architecture is a framework that allows software professionals to describe and communicate software architectures with diagrams. It was created by Simon Brown and is composed of four levels: Context, Containers, Components, and Code. Each level zooms in on the software system, providing a more detailed view. This guide covers the high-level concepts of the C4 model and includes examples based on a fictitional online bank.

Overview​

  1. Context: Focuses on the high-level view of the system; shows how the software system fits into the real-world environment, including external systems and users.
  2. Containers: Delves into the system, showcasing the high-level technology choices, how containers communicate, and their responsibilities.
  3. Components: Further breaks down the containers into individual components, illustrating how a specific container is composed and how components interact.
  4. Code: The most granular level of the model, focusing on the code level inside the components.

Context​

High-Level Concepts​

  • Purpose: Understand how your system interacts with external entities and fits into the larger environment.
  • Elements: Include your system, users, and external systems your system interacts with.
  • Scope: Keep the details minimal; the goal is to understand the overall interactions.

Example​

A context diagram for the Internet Banking System might include:

  • "Personal Banking Customer" as the user
  • "Internet Banking System" for customer interactions
  • "Mainframe Banking System" for core banking functionalities
  • "Email System" for communication

Context Diagram

Container​

High-Level Concepts​

  • Purpose: A closer look at the high-level internal structure of the system and how containers (applications, databases, etc.) within the system interact.
  • Elements: Applications, data stores, databases, and more, along with the technology used (e.g., WebSockets, HTTP, relational database).
  • Scope: High-level; avoid delving into component details.

Example​

A container diagram for the Internet Banking System might include:

  • "Web Application" for user interaction, using HTML/JavaScript.
  • "Single-Page Application" for a more responsive user interface.
  • "Mobile App" for banking on the go.
  • "API" for application-system interaction.

Container Diagram

Component​

High-Level Concepts​

  • Purpose: Breaks down the internal structure of a specific container.
  • Elements: Components/services and their interactions.
  • Scope: Detailed; showcases the functionality of each component inside a container.

Example​

A component diagram for the facade might include:

  • "MainframeBankingSystemFacadeImpl" for creating and parsing requests/responses.
  • "BankingSystemConnection" for sending/receiving data.

Component Diagram

Code​

High-Level Concepts​

-Purpose: Focus on the code-level view of a component. -Elements: Classes, interfaces, entities, and their relationships. -Scope: Very detailed; suitable for developers needing to understand the code structure.

Example​

Given the "MainframeBankingSystemFacadeImpl" component, a code diagram might show:

  • Specific methods for creating/parsing requests.
  • Handlers for sending/receiving data.
  • Interfaces for data transmission.

Code Diagram

Conclusion​

The C4 model provides a multi-level, hierarchical approach for diagramming software architectures, moving from broad system interactions to detailed code structures. It helps diverse stakeholders understand the system at various depths, promoting clarity and reducing confusion.