Enhancing Software Architecture Documentation with Arc42 and the C4 Model

In the dynamic realm of software development, clear and comprehensive architecture documentation is paramount. This article explores how combining Arc42 and the C4 Model can streamline this process, offering a structured approach to documenting software architectures.

Solutions for Software Architecture Documentation

Several methodologies and tools have been developed to streamline this process, each offering unique approaches to capturing and conveying architectural information.

ISO/IEC/IEEE 42010: Also known as the IEEE Recommended Practice for Architectural Description of Software-Intensive Systems, this standard provides guidelines on architectural descriptions for software systems.

The 4+1 View Model: This model is widely adopted because it provides a comprehensive and structured way to describe software architecture. Its use of multiple views helps address different stakeholders' concerns effectively.

C4 Model: Created by Simon Brown, it is a hierarchical way of visualizing the architecture of software systems, focusing on different levels of detail. The main purpose of the C4 model is to enhances the understanding of system architecture through visual representation.

Arc42: ?A Comprehensive and flexible template widely used for documenting software architecture, providing clear sections that cover a broad spectrum of architectural concerns

TOGAF (The Open Group Architecture Framework): TOGAF provides a structured approach for designing, planning, implementing, and governing enterprise information architectures.

Dragon1: A (Paid) platform that provides tools and methods for creating architecture visualizations and documentation. It includes templates and guidelines for documenting various aspects of architecture.

DoDAF (Department of Defense Architecture Framework) and MODAF (Ministry of Defence Architecture Framework): These are frameworks used primarily in government contexts (US and UK respectively) for architecture documentation in defense and related domains.

The high-level, 6-step architecture development process provides guidance to the architect and architectural description development team and emphasizes the guiding principles.

Arc42 vs. Other Standards

This section presents a comparative overview of Arc42 and other notable standards, highlighting their key features and differences.

Why Choosing Arc42

Selecting an appropriate framework for software architecture documentation is crucial for ensuring clarity, consistency, and effective communication among stakeholders.

Arc42 stands out as a preferred choice due to several key criteria that align with the diverse needs of development teams:

• Comprehensive Coverage: Covers all aspects of software architecture in a structured manner.
• Flexibility: Can be adapted to various project sizes and types.
• Community Support: Large community, extensive documentation, and examples.
• Practicality: Provides concrete templates that guide the documentation process.
• Compatibility: Can be used alongside other models and methodologies, like the C4 model.
• Everything is optional - there is no need to fill in every section of the template
• Completely tool agnostic. You might create and maintain arc42 in your tool chain of choice: A wiki, a collection of Office documents, plain Markdown or Asciidoc, one of the commercial UML tools or even LaTeX.

Arc42 Template Structure

Tailored into 12 separate chapters, each addressing a certain software architecture aspect.

Purpose: Provides a clear, structured way to capture architecture-related information.

It is not only a collection of headlines. Each aspect is equipped with additional information, regarding:

?Content →?What?should be documented?

?Motivation →?Why?should it be documented?

?Form →?How?should it be documented?

1.Introduction and goals

Short description of:

• The requirements and driving forces of your system
• Main quality attributes that the system needs to achieve
• Stakeholders with their expectation regarding architecture or documentation.

2. Constraints

Anything that constrains teams in design and implementation decisions, or decision about related processes.

Constraints can sometimes go beyond individual systems and might valid for whole organizations and companies (e.g. company-wide technology choices or government regulations).

Decisions already taken.

3. Context and scope

Delimits your system from its (external) communication partners (neighboring systems and users). Specifies the external interfaces. Shown from a business/domain perspective (always) or a technical perspective (optional).

4. Solution strategy

Summary of the fundamental decisions and solution strategies that shape the architecture:

Can include:

• Technology
• Top-level decomposition
• Approaches to achieve top quality goals
• Relevant organizational decisions.

5. Building block view

Explains Static decomposition of system:

Modules of the system

Hierarchy of white boxes containing black boxes

Start with overall overview diagram

Decompose into other diagrams

• Level 0: scope and context
• Level 1: contains the major subsystems, components or parts of the system.?In some cases, this coarse overview provides enough structural overview.
• Level 2: refines one or more elements from level 1: Create a separate white box (plus explanations) for every level-1 building block you would like to explain in detail

You can drill down to an arbitrary level of detail, but keep in mind the following:

Recommendation Try to stick to level-1, as it often gives enough guidance and understanding for most stakeholders.

6. Runtime view

Explains the behavior or processing of one or several building blocks. It serves as companion to the static building block view from section 5 above.

The runtime view might explain important use cases or features, interactions at critical external interfaces, error and exception behavior.

Format:

• Natural language (list of steps)
• UML sequence diagrams
• Flowcharts
• BPMN

7. Deployment view

Shows the technical infrastructure with environments, computers, processors, networks and network-topologies.

Mapping of (software) building blocks to infrastructure

Format:

• UML deployment diagrams
• Mapping tables

8. Cross-cutting concepts

Overall, principal regulations and solution approaches relevant in multiple parts (cross-cutting) of the system.

Concepts are often related to multiple building blocks.

Include different topics like:

• Domain models,
• Architecture patterns and -styles,
• Rules for using specific technology,
• Implementation rules.

9. Architecture decisions

Collection of architecturally significant decisions that are important,? expensive, critical, large scale or risky including rationales, that are not recorded elsewhere.

Format:

• List or table ordered by importance
• Architecture Decision Records for important decisions

Note: The most important decisions of architecture may have already captured in the solution strategy.

10. Quality requirements

Quality requirements, often described as scenarios.

Use a quality tree to provide a high-level overview.

The most important quality goals should have been already described in section 1.2. (quality).

10.1 Quality tree

A quality tree with quality scenarios as leafs

Include priorities for an overview

Sometimes, large number of quality requirements.

Format:

• A mind map with quality categories as branches
• Include links to scenarios of the following section

10.2 Quality scenarios

Scenarios describe what should happen when a stimulus arrives at the system.

2 Types:

• Usage: runtime reaction to a certain stimulus.

?? "The system reacts to a user’s request within 1 sec."

• Change: modification of the system or its environment

??? "A new user type must be added“

Format:

• Tabular or free form text

11. Risks and technical dept requirements

Known technical risks or technical debt.

?????????? What potential problems exist within or around the system?

?????????? What does the development team feel miserable about.

Format:

• List or risks/technical debts
• Include suggested measures to minimize, mitigate or avoid risks or reduce technical debts

Note: In case somebody reviewed or audited your system, their findings might be included here.

12. Glossary

Important domain and technical terms that stakeholders use when discussing the system.

Include only specific terms (Common vocabulary) and avoid explaining REST, HTTPS or other words that have common explanations.

The glossary can serve as the translation reference if you work in a multi-language (international) environment.

Format:

• Table

Using the C4 Model with Arc42

Complementary Nature:

• arc42 provides the detailed narrative and textual documentation.
• C4 Model offers visual representations to complement the textual documentation

Integration:

• Use C4 diagrams within the arc42 template sections like Building Block View and Runtime View.

Align the levels of C4 diagrams with the layers of arc42 documentation.

Benefits:

• Provides a comprehensive, multi-faceted view of the system architecture.
• Enhances clarity and understanding for both technical and non-technical stakeholders.
• Supports both high-level overviews and detailed insights.

The integration mapping as follows:

Modularization extensive documentation with Arc42

The overall systems is made up from three subsystems.

Each subsystems’ documentation contains only parts of the arc42 template, and each subsystem focuses on different aspects.

High-Level Design (HLD) in arc42

The HLD typically focuses on the overall architecture, main components, and their interactions.

In the arc42 template, HLD information is distributed across several sections:

1.Introduction and Goals
   Overview of the system
   Goals and objectives
  Stakeholders
2.Architecture Constraints
   Technical constraints
   Organizational constraints
   Conventions and standards
3.Context and Scope
   Business context
   Technical context
   Scope and boundaries
4.Solution Strategy
   Key design decisions
   Architectural patterns
   Rationale for decisions
5.Building Block View
   Overview of building blocks
   Level 1
7.Deployment View
   Infrastructure and environment
   Deployment diagram
   Scalability and performance considerations
        

Low-Level Design (LLD) in arc42

The LLD provides detailed descriptions of components, their interactions, and implementation details.

In the arc42 template, LLD information is primarily found in:

5.Building Block View
   Level 2
   Level 3
6.Runtime View
  Detailed runtime scenarios
  Sequence diagrams
   Interaction diagrams
7.Deployment View
  Detailed deployment information
  Configuration of infrastructure components
8.Crosscutting Concepts
  Security
  Performance
  Scalability
  Other crosscutting concerns
        

Conclusion

arc42 and C4 Model offer a powerful combination for documenting software architecture.

arc42 provides detailed templates, while C4 Model adds visual clarity.

Together, they ensure comprehensive, clear, and maintainable architecture documentation.