Week 6 Part III · Architecture and Patterns

Layered Architecture and Application Structure

Instructor lesson plan: lecture (2 h) and practice (2 h).

Learning objectives

Separate presentation, application, domain, and infrastructure concerns.
Define project references that enforce dependency direction.
Move use-case logic out of controllers and persistence classes.
Document an application structure that supports change.

Tools this week

solution foldersproject referencesdependency rulesC4 diagrams

🎓Lecture · 2 hours

0:00-0:15	15 min	Proposal feedback synthesisCommon scope and boundary issues from week 5.
0:15-0:40	25 min	The four common layers Presentation, application, domain, infrastructure. Responsibilities and examples in the semester project.
0:40-1:05	25 min	Dependency direction Who may reference whom, and why. Keeping infrastructure replaceable.
1:05-1:15	10 min	DTOs, commands, and servicesApplication input and output models versus API models.
1:15-1:25	10 min	Break
1:25-1:50	25 min	C4 diagramsSystem context, containers, and component diagrams for student systems.
1:50-2:00	10 min	Practice previewRestructure the project without breaking behavior.

Common misconception to confront.

Students often think: layers are just folders.
Set it straight: layers are dependency and responsibility rules. Folders without rules do not create architecture.

Check for understanding

Why should domain not reference infrastructure?

The domain should express business rules without depending on databases, HTTP clients, files, or framework details.

Where does a use case usually live?

In the application layer, coordinating domain behavior, persistence abstractions, validation, and output models.

Key takeaways.

Architecture is enforced by dependencies.
Controllers should stay thin.
Diagrams make structure reviewable.

📚Reading & resources

Common web application architectures Microsoft guidance on layered and clean architectures.
C4 model Diagramming approach for software architecture.

💻Practice · 2 hours

0:00-0:20	20 min	Dependency mapDraw current project references and identify violations.
0:20-0:55	35 min	Restructure solutionMove code into presentation, application, domain, and infrastructure projects.
0:55-1:10	15 min	Compile and inspectFix reference direction and keep behavior intact.
1:10-1:20	10 min	Break
1:20-1:50	30 min	Diagram updateCreate a C4 container or component sketch for the new structure.
1:50-2:00	10 min	Project-integration briefSubmit the revised structure and diagram.

Project integration (this week)

Reorganize the project into explicit layers.
Move use cases into the application layer.
Add a diagram showing dependency direction.